Microstructure-based optical diffusers for creating batwing and other lighting patterns

ABSTRACT

A light transmissive structure includes a light transmissive substrate having first and second opposing faces and array of microprism elements on the first face, with a respective microprism element including a plurality of concentric microprisms. The light transmissive structure is configured to receive light from a light source facing the first face and distribute the light emerging from the second face in a 2D batwing distribution.

RELATED APPLICATION

This application claims priority from U.S. Provisional Application No.61/836,822, filed Jun. 19, 2013, the disclosure of which is herebyincorporated herein in its entirety.

BACKGROUND

Various embodiments described herein relate to light sources,particularly luminaires, for providing special lighting patterns. Theseembodiments have particular, but not exclusive, usefulness in providingwhat is known in the art as “batwing” lighting patterns.

In many illumination systems, targeted areas to be illuminated are muchlarger than an emitting area of the light sources. Many artificial lightsources emit light in an approximately Lambertian distribution. Whenilluminated from above by such a source, flat targeted areas such asroads, floors, or a work surface cannot be illuminated uniformly withoutmodifying the intensity distribution of the light source. When a lightsource with Lambertian intensity distribution illuminates a flat surfacefrom above, the intensity on that surface will be greatest directlyunder the light source, and will decrease monotonically for points onthe surface farther away. A “batwing” distribution, conversely, reducesthe intensity at nadir (directly under the light source) and increasesthe intensity at angles up to some maximum angle, such that the surfaceis illuminated substantially uniformly for angles less than the maximumangle. Batwing light distributions can exist in several forms:one-dimensional (1D) batwings have a batwing shape only to the sides(e.g. East-West direction) and are often used with linear lighting.Two-dimensional (2D) circular batwing distributions create a batwing“cone” of light, illuminating evenly in all radial directions to achievea disc-shaped area of uniform illumination on a flat surface. 2D squareor rectangular batwings create a batwing “pyramid” of light,illuminating evenly in both North-South and East-West directions toachieve a square- or rectangular-shaped area of uniform illumination ona surface, substantially filling in dark corners between luminairesarrayed in a square or rectangular array on a ceiling. Because it iscommon to light areas such as warehouses and offices using lightingfixtures in a rectangular array on a ceiling, the rectangular batwinglight distribution is highly desirable. Frequently luminaires withbatwing distributions can provide the desired uniformity of illuminationat a greater luminaire-to-luminaire spacing than with Lambertianluminaires, meaning that fewer luminaires are necessary to illuminatethe desired area, saving cost. In addition, the nadir suppressioninvolved in a batwing distribution means minimum lighting levels can bemet across the surface without far exceeding that minimum level at thenadir, which would unnecessarily waste energy.

A downward-facing light source with Lambertian light distribution hasluminous intensity that is proportional to the cosine of the angle fromnadir (the downward-facing direction). A Lambertian light distributionis represented in polar coordinates in FIG. 1. When a flat surface suchas a floor is illuminated by a Lambertian light distribution, theilluminance on the floor is greatest at nadir (directly under thefixture) and decreases monotonically for points on the floor away fromnadir. The central brightness is often referred to as a “hot spot” inthe lighting industry, and is generally undesirable. By definition, theFull Width at Half Maximum (FWHM) of a Lambertian distribution is 120degrees. In the lighting industry, the term “Lambertian” is alsofrequently used to refer to light distributions with similar quality butof different widths. That is, distributions that have a peak at nadir,and monotonically decrease at higher angles are often called Lambertian.In one example, a Gaussian distribution with FWHM of 80 degrees willoften be called “Lambertian” in the lighting industry. Lambertiandistributions are not batwing distributions.

For a single ceiling luminaire, which is small compared to theceiling-to-floor distance, to uniformly illuminate a specified widthacross a flat surface such as a floor, it generally must emit light in abatwing distribution whose luminous intensity is inversely proportionalto the cube of the cosine of the angle from nadir for angles less thanthe maximum angle. This theoretical distribution can be represented bythe solid curve in FIG. 2, in which no light extends beyond the maximumangle. In practice, multiple luminaires are generally used to illuminatea surface such as a room, warehouse, or roadway, and it is desirable tohave some overlap, or crossfade, between the light distributions emittedby each light source. Thus a practical batwing light distribution oftenhas some light extending beyond the maximum angle, as illustrated in thedashed curve of FIG. 2. The sharp “peaks” of the light distribution inthe solid curve are also disadvantageous because they can be noticeableto a viewer, and are hard to create in practice. The dashed curve ofFIG. 2 shows more practical rounded peaks in the light distribution.

In practice, it is acceptable to have some level of variation of theilluminance on a surface. For various lighting applications, anilluminance variation of about 50%, 20%, 10%, 5%, or less may beacceptable across the surface of interest when illuminated by an arrayof luminaires. Because the specified level of variation allows for somedeviation from ideal conditions, the batwing diffuser is allowed to havea light distribution that doesn't exactly follow the 1/cos³distribution. This imperfection is illustrated in central portion of thedashed curve in FIG. 2.

In lighting, batwing light distributions different from the typicalinverse cosine cubed shape are also used. These may be desired, forexample, in a library or store, in which it may be desired to illuminatevertical surfaces of shelves holding books or items. For these and otherlighting applications, a degree of nadir suppression may be desirablethat is greater or less than the typical inverse cosine cubed shape.

High-efficiency LED lighting is being increasingly adopted. Typical LEDlight sources emit light into a Lambertian distribution with a FullWidth Half Max (FWHM) of approximately 120 degrees. Although LEDs withmany other light distributions are available, many cost-effective LEDssold for general lighting are of the 120 degree Lambertian variety. Manyluminaires (LED and traditional) have flat outer surfaces (such as somedownlights, task lights, and troffers). In many of these fixtures, asimple flat diffuser (such as a microstructured, holographic, orvolumetric diffuser) is used to diffuse the LEDs, hiding theirappearance from viewers and smoothing the surface appearance of theluminaire. These diffusers do not produce 2D batwing distributions.Rather, they typically give Lambertian distributions of various widths(most typically about 80 to 120 degrees).

SUMMARY

Light transmissive structures according to various embodiments describedherein include a light transmissive substrate having first and secondopposing faces and array of microprism elements on the first face, witha respective microprism element comprising a plurality of concentricmicroprisms. The light transmissive structure is configured to receivelight from a light source facing the first face and distribute the lightemerging from the second face in a 2D batwing distribution.

In some embodiments, the array of microprism elements extends oversubstantially the entire first face of the substrate.

In some embodiments, a respective microprism element includes aplurality of concentric circular microprisms. At least some of themicroprisms may have a generally triangular cross section with a peak,with the cross section taken in a plane perpendicular to the first faceof the substrate, and may have a prism internal angle defined by thepeak that varies as a function of a prism orientation angle that ismeasured relative to an edge of the substrate. In some embodiments,portions of the microprisms having prism orientation angles of about 45degrees and 135 degrees have a prism internal angle that is less than aprism internal angle of portions of the microprisms having prismorientation angles of about 0 degrees and 90 degrees.

In some embodiments, a respective microprism element includes aplurality of concentric elliptical microprisms.

In some embodiments, a respective microprism element includes aplurality of concentric rounded square microprisms. A respective roundedsquare microprism may have a shape that fits between a square and itsinscribed circle. At least some of the microprisms may have a generallytriangular cross section with a peak, with the cross section taken in aplane perpendicular to the first face of the substrate, and may have aprism internal angle defined by the peak that varies as a function of aprism orientation angle that is measured relative to an edge of thesubstrate. In some embodiments, portions of the microprisms having prismorientation angles of about 45 degrees and 135 degrees have a prisminternal angle that is less than a prism internal angle of portions ofthe microprisms having prism orientation angles of about 0 degrees and90 degrees.

In some embodiments, a respective microprism element is generallyhexagonal. In some embodiments, a respective microprism element isgenerally square.

In some embodiments, a respective microprism element includes aplurality of concentric rounded rhombus microprisms. A respectiverounded rhombus microprism may have a shape that fits between a rhombusand its inscribed ellipse. At least some of the microprisms may have agenerally triangular cross section with a peak, with the cross sectiontaken in a plane perpendicular to the first face of the substrate, andmay have a prism internal angle defined by the peak that varies as afunction of a prism orientation angle that is measured relative to anedge of the substrate.

A respective microprism element may include concentric microprisms ofrandom or pseudorandom size and/or shape. A respective microprismelement may be longer in a first direction along the substrate than in asecond, orthogonal direction along the substrate.

In some embodiments, a respective microprism element has an area of lessthan about 1 square centimeter on the second face of the substrate. Insome embodiments, a respective microprism element has an area of about0.1 square centimeters or less on the second face of the substrate. Insome embodiments, a respective microprism is undetectable by the nakedeye.

In some embodiments, at least some of the microprisms have a generallytriangular cross section with a peak, with the cross section taken in aplane perpendicular to the first face of the substrate. The peak may begenerally parallel to the first face of the substrate. The peak may be asharp peak. The peak may be a rounded peak. In some embodiments, (i) arespective microprism has an internal angle defined by the peak ofbetween about 60 and 100 degrees; and/or (ii) a respective microprismhas a pitch of between about 10 microns and 3 mm. In some embodiments,(i) a respective microprism has an internal angle of between about 70and 90 degrees; and/or (ii) a respective microprism has a pitch ofbetween about 10 microns and 1 mm.

In some embodiments, substantially all of the microprism elementsinclude a plurality of concentric microprisms.

In some embodiments, adjacent microprism elements are in contact withone another.

In some embodiments, the array of microprism elements includes gapsbetween at least some of the microprism elements, and the lighttransmissive structure further includes gap-filling microstructures inat least some of the gaps.

In some embodiments, at least some of the microprisms have a generallytriangular cross section with a peak, with the cross section taken in aplane perpendicular to the first face of the substrate, and with thepeak having a height relative to the first face of the substrate thatvaries as a function of a prism orientation angle that is measuredrelative to an edge of the substrate.

In some embodiments, the light transmissive structure is configured toreceive light having a Lambertian distribution from a light sourcefacing the first face and distribute the light emerging from the secondface in a 2D batwing distribution. In some embodiments, the lighttransmissive structure is configured to receive light having a lightdistribution having a Full Width at Half Maximum (FWHM) of at leastabout 30 degrees from a light source facing the first face anddistribute the light emerging from the second face in a 2D batwingdistribution. In some embodiments, the light transmissive structure isconfigured to receive light having a light distribution having a FullWidth at Half Maximum (FWHM) of at least about 40 degrees from a lightsource facing the first face and distribute the light emerging from thesecond face in a 2D batwing distribution. In some embodiments, the lighttransmissive structure is configured to receive light having a lightdistribution having a Full Width at Half Maximum (FWHM) of at leastabout 60 degrees from a light source facing the first face anddistribute the light emerging from the second face in a 2D batwingdistribution.

In some embodiments, the light transmissive structure is configured toreceive light having a light distribution having a Full Width at HalfMaximum (FWHM) of at least about 80 degrees from a light source facingthe first face and distribute the light emerging from the second face ina 2D batwing distribution.

In some embodiments, the light transmissive structure includes at leastone diffusion feature, and the light transmissive structure isconfigured to receive collimated and/or near-collimated light from alight source facing the first face and distribute the light emergingfrom the second face in a 2D batwing distribution. The diffusion featuremay include surface roughness on at least some of the microprisms. Thediffusion feature may include a diffuser on the second face of thesubstrate. The diffusion feature may include a light scattering agent inat least some of the microprisms and/or in the substrate. The diffusionfeature may include a diffusive coating on at least some of themicroprisms.

In some embodiments, a respective microprism follows a prism path alongthe first face of the substrate. The microprism may have a generallytriangular cross section with a peak and a pitch, with the cross sectiontaken in a plane perpendicular to the first face of the substrate. Thepeak may have a height relative to the first face of the substrate thatvaries along the prism path and/or the pitch may vary along the prismpath.

In some embodiments, the light transmissive structure is in combinationwith at least one light source and a housing that is configured to holdthe at least one light source and the light transmissive substrate sothat light from the light source impinges on the first face of thesubstrate and emerges from the second face of the substrate in a 2Dbatwing distribution. The housing may define a light exit surface areawhere the substrate is held. In various embodiments, a respectivemicroprism element has an area on the first face of the substrate thatis at least one order or magnitude, at least two orders of magnitude,and/or at least four orders of magnitude smaller than the light exitsurface area. In some embodiments, the array of microprism elements onthe first face of the substrate extends over substantially the entirelight exit surface area.

In some embodiments, the light transmissive structure is in combinationwith at least one light source wherein the light transmissive substrateis suspended under the light source so that light from the light sourceimpinges on the first face of the substrate and emerges from the secondface of the substrate in a 2D batwing distribution.

Light transmissive structures may be fabricated according to variousembodiments described herein by imaging onto a photoimageable materialan image of a plurality of microprisms having a geometric feature thatis configured to distribute light transmitted through the microprisms ina 2D batwing distribution. The photoimageable material that was imagedis then used to replicate an image of a plurality of microprisms inand/or on a substrate, the plurality of microprisms also having ageometric feature that is configured to distribute light transmittedthrough the microprisms in a 2D batwing distribution. The imaging may beperformed by scanning a laser across the photoimageable material, thelaser defining the image of a plurality of microprisms having thegeometric feature that is configured to distribute light transmittedthrough the microprisms in a 2D batwing distribution.

Light transmissive structures according to various embodiments describedherein include a light transmissive substrate having first and secondopposing faces. A plurality of microprisms are on the first face, withthe microprisms having a generally triangular cross section in a planethat is perpendicular to the first face, and the microprisms aredistributed on the first face of the substrate in a plurality ofdifferent prism orientation angles measured from an edge of thesubstrate. The light transmissive structure is configured to receivelight having a Full Width at Half Maximum (FWHM) of at least about 30degrees and/or Lambertian light at the first face and distribute thelight emerging from the second face in a 2D batwing distribution. Insome embodiments, the light transmissive structure is configured toreceive light having a Full Width at Half Maximum (FWHM) of at leastabout 40 degrees and/or Lambertian light at the first face anddistribute the light emerging from the second face in a 2D batwingdistribution.

In some embodiments, the microprisms are distributed on the first faceof the substrate generally equally in each of the plurality prismorientation angles. In some embodiments, microprisms having a prismorientation angle of about 45 and 135 degrees are distributed on agreater area of the first face of the substrate than microprisms havinga prism orientation angle of about 0 and 90 degrees. In someembodiments, the microprisms have an internal angle that varies as afunction of prism orientation angle. In some embodiments, the pluralityof microprisms and/or interspersed microstructures substantially coverthe first face of the substrate.

Light transmissive structures according to various embodiments describedherein include a light transmissive substrate having first and secondopposing faces. An array of microprism elements is on the first face,with a respective microprism element including a plurality of concentricmicroprism patterns, and with a respective microprism pattern includinga plurality of pyramids arranged in a generally ellipticalconfiguration. The light transmissive structure is configured to receivelight from a light source facing the first face and distribute the lightemerging from the second face in a 2D batwing distribution.

It is noted that any one or more aspects or features described withrespect to one embodiment may be incorporated in a different embodimentalthough not specifically described relative thereto. That is, allembodiments and/or features of any embodiment can be combined in any wayand/or combination. Applicant reserves the right to change anyoriginally filed claim or file any new claim accordingly, including theright to be able to amend any originally filed claim to depend fromand/or incorporate any feature of any other claim although notoriginally claimed in that manner. These and other objects and/oraspects of the present invention are explained in detail in thespecification set forth below.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a chart illustrating a Lambertian intensity distribution witha Full Width Half Maximum (FWHM) of 120 degrees.

FIG. 2 is a chart illustrating theoretical and practical batwingdistributions.

FIG. 3A is a cross-sectional view of collimated light impinging a linearprism film.

FIG. 3B is a chart illustrating a Lambertian light source distribution(dotted curve) and the 1D split distribution of the Lambertian lightsource after passing through the linear prism film of FIG. 3A with theprism texture facing the light source (solid curve).

FIG. 4 is a chart illustrating the measurement of light distributions ina spherical coordinate system.

FIG. 5 is a chart illustrating the light distribution of a Lambertianlight source after passing through a linear prism film with prismtexture facing the light source.

FIG. 6A is a chart illustrating the light distribution of a Lambertianlight source after passing first through a linear prism film and thenthrough a 30 degree FWHM diffuser.

FIG. 6B is a chart illustrating the light distribution of a Lambertianlight source after passing first through a linear prism film and thenthrough a 55 degree FWHM diffuser.

FIG. 7 is a chart illustrating the light distribution of a Lambertianlight source having a FWHM of 120 degrees after passing through a filmhaving an array of closely-packed cones facing the light source.

FIG. 8 is a chart illustrating the light distribution of anear-Lambertian light source having a FWHM of 80 degrees after passingthrough a film having an array of closely-packed cones facing the lightsource.

FIG. 9 is a chart illustrating the light distribution of a collimatedlight source after passing through a film having an array ofclosely-packed cones facing the light source.

FIG. 10 is a chart illustrating the light distribution of anear-collimated light source having a FWHM of 20 degrees after passingthrough a film having an array of closely-packed cones facing the lightsource.

FIG. 11 is a perspective view of a substrate having prisms orientedthereon in different prism orientation angles.

FIG. 12 includes a perspective view of a substrate having curved prismsoriented thereon and a cross-sectional view of the prisms.

FIG. 13 is an enlarged fragmentary perspective view of a lighttransmissive structure including an array of microprism elementsaccording to some embodiments described herein.

FIG. 14 is a chart illustrating the light distribution of a Lambertianlight source having a FWHM of 120 degrees after passing through thelight transmissive structure of FIG. 13 with the microprism elementsfacing the light source.

FIG. 15 is a chart illustrating the light distribution of a light sourcehaving a FWHM of 40 degrees after passing through the light transmissivestructure of FIG. 13 with the microprism elements facing the lightsource and having microprisms with a prism internal angle of about 90degrees.

FIG. 16 is a chart illustrating the light distribution of a light sourcehaving a FWHM of 40 degrees after passing through the light transmissivestructure of FIG. 13 with the microprism elements facing the lightsource and having microprisms with a prism internal angle of about 70degrees.

FIG. 17 is an enlarged fragmentary perspective view of a lighttransmissive structure including an array of microprism elementsaccording to some embodiments described herein.

FIG. 18 includes an enlarged fragmentary perspective view of one of themicroprism elements of FIG. 17 modified to have microprisms having aprism internal angle that varies as a function of prism orientationangle and cross-sectional views of the prisms.

FIG. 19A is a chart illustrating the light distribution of a lightsource having a FWHM of 40 degrees after passing through the lighttransmissive structure of FIG. 18 with the microprism elements facingthe light source.

FIG. 19B is a contour plot of the illumination on a flat surface causedby the light distribution of FIG. 19A.

FIG. 20 is a chart illustrating the light distribution of a light sourcehaving a FWHM of 80 degrees after passing through the light transmissivestructure of FIG. 18 with the microprism elements facing the lightsource.

FIG. 21 is an enlarged fragmentary perspective view of a lighttransmissive structure according to some embodiments described herein.

FIG. 22 is an enlarged fragmentary perspective view of a lighttransmissive structure according to some embodiments described herein.

FIG. 23 is a perspective view of a light transmissive structure and apattern element having an area thereon.

FIG. 24 is a chart illustrating the relative sizes of a luminaire, apattern element and a prism according to some embodiments describedherein.

FIG. 25A is a plan view a light transmissive structure according to someembodiments described herein.

FIG. 25B is a plan view of a light transmissive structure that is anapproximation of the light transmissive structure of FIG. 25A accordingto some embodiments described herein.

FIG. 26 is a chart illustrating the light distribution of a Lambertianlight source after passing first through the light transmissivestructure of FIG. 25B with the prism side facing the light source andthen through a 15 degree FWHM diffuser.

FIG. 27A is a plan view illustrating the light transmissive structure ofFIG. 25B centered upon a light exit opening.

FIG. 27B is a plan view illustrating the light transmissive structure ofFIG. 25B misaligned with a light exit opening.

FIG. 28 is a chart illustrating the light distribution using theconfiguration of FIG. 27B.

FIG. 29 is a plan view of a light transmissive structure according tosome embodiments described herein.

FIG. 30 is a plan view of a light transmissive structure according tosome embodiments described herein.

FIG. 31 is a chart illustrating the light distribution of a light sourcehaving a FWHM of 40 degrees after passing through the light transmissivestructure of FIG. 30 with the prism side facing the light source.

FIGS. 32-39 are simplified cross-sectional views of luminaires accordingto various embodiments described herein.

FIG. 40 is a chart illustrating the light distribution of asubstantially collimated light source after passing through the lighttransmissive structures according to various embodiments describedherein.

FIG. 41 is an enlarged fragmentary perspective view of a lighttransmissive structure according to some embodiments described herein.

FIG. 42A is a chart illustrating the light distribution of anear-collimated light source after passing through the lighttransmissive structures according to various embodiments describedherein.

FIG. 42B is a chart illustrating the light distribution of anear-collimated light source after passing through the lighttransmissive structures according to various embodiments describedherein with added surface roughness.

FIG. 43 is a flowchart of methods of fabricating light transmissivestructures according to various embodiments described herein.

FIG. 44A is a cross-sectional view of a light transmissive structureaccording to some embodiments described herein.

FIGS. 44B-44H are cross-sectional views of light transmissive structureswith added diffusion features according to various embodiments describedherein.

FIG. 45 is an enlarged fragmentary perspective view of a lighttransmissive structure according to some embodiments described herein.

FIG. 46 is an enlarged fragmentary perspective view of a lighttransmissive structure according to some embodiments described herein.

DETAILED DESCRIPTION

For collimated light, beam shaping is well known in the art. Refractiveand diffractive elements exist that can form a (collimated) laser beaminto a specific shape. Such elements are available commercially, forexample, from Jenoptik, Jena, Germany(http://www.jenoptik.com/en-microoptics-refractive-optical-elements-ROEs).These elements can shape a laser beam into a line, crosshair, square,circle, and even images (such as corporate logos) to project on asurface, and are commonly used in machine-vision applications. Beamshapers generally require substantially collimated light. As is shown bythe review of prior art herein, a shaper does not appear to currentlyexist that can convert a Lambertian distribution into a 2D batwingdistribution, despite the value the lighting industry would place onhaving such a product.

A 90-degree linear prism optic has one smooth surface and the other oneis textured by an array of linear prisms with 45-degree sidewalls, asshown in U.S. Pat. No. 3,288,990 and U.S. Pat. No. 4,542,449, in whichone or two layers of prism optics are used to increase brightnessdirectly under a luminaire, and reduce high-angle brightness. A filmwith the same properties is described in U.S. Pat. No. 4,906,070. Acommon application of such a prism film is for brightness enhancement ofthe back light unit inside a display system. In both lighting anddisplays, a brightness-enhancing prism is used with the light enteringsmooth surface of the optic, and thus the prisms facing away from thelight source. Rays incident perpendicular to the surface of the filmwill encounter total internal reflections (TIR) from the prisms. Thoselight rays are generally reflected back into the backlight, which isgenerally configured with high reflectivity to recirculate those raysback toward the prism film (sometimes repeatedly), until they enter theprism film at larger incident angle and are allowed to pass to theviewer of display. Rays incident at larger angles are at least in partrefracted through the prisms, and on average over all angles, theaverage exit angles are smaller than the average entrance angles, whenmeasured relative to the normal to the prism optic. The angle bendingand recirculation process creates a narrower FWHM light distribution(approx 70-95 degrees) than the incident Lambertian distribution (approx120 degrees), and on-axis brightness enhancement. Said another way, aprism illuminated by Lambertian light in this orientation and withappropriate recirculation will increase intensity at the nadir, whilereducing the FWHM. Thus, a prism used in this manner does not create abatwing distribution.

In contrast, it is known that if the light enters the prism side (ratherthan the smooth side) of a linear prism film or optic, it will exit intwo lobes, similar to a 1D batwing shape (as mentioned in U.S. Pat. No.4,300,185 or U.S. Pat. No. 4,233,651). FIG. 3A illustrates howcollimated light will be divided (refracted) into two branches by prismstructures. The angular deviation of this refraction is determined bythe refractive index of the material, and the sidewall angle of theprisms. Typical refractive indices for prism films are in the range of1.45 to 1.6. Smaller prism internal angle or greater refractive indexwill result in larger refraction angles. Even Lambertian light impingingonto the prism side of a linear prism film will exit that film in a 1Dsplit distribution, in which light is approximately a batwing shape.This use of a linear prism is referenced on the Fusion Optix website athttp://fusionoptix.com/lighting/components/light-shapers.htm (as of May17, 2013), a diagram adapted from which is shown in FIG. 3B. Thereduction of light intensity at theta (θ)=0 degrees (straight down inthe image) is called “nadir suppression.”

Measurement

Light distributions are typically measured using goniometric apparatussimilar to that described in the IES LM-79 standard, as illustrated inFIG. 4. In the figure, a luminaire or illuminated optical device isdepicted (labeled SSL product) emitting light in a downward dimension.The two circles with dots on their perimeters represent planes at twodifferent azimuthal angles φ (phi). In each of these planes, the polarangle θ (theta, ranging from −180 to 180 degrees) is defined asindicated. Example measurement points in the phi=0 degree and phi=90degree planes are depicted as dots. At each of these points, luminousintensity is measured as a function of the theta angle from theprinciple axis of the light source. This luminous intensity is measureby an optical detector, the optical detector and/or light source movedrelative to each other so that the optical detector measures light atthe desired angles. In practice a light source can be measured at anygroup of phi and theta points desired. Many lights emit generally in onehemisphere, and thus theta will often be measured from −90 to 90degrees.

Confirming the data presented in FIG. 3B, FIG. 5 shows the lightintensity distribution measured by the applicant by illuminating a flatprism film with a Lambertian LED light source, with the prism sidefacing the light. The solid line represents the measurement made in aplane designated phi=90 degrees that is perpendicular to the orientationof the linear prisms on the prism film. The dashed line shows the phi=0degree plane parallel to the prism orientation, and shows the outputdistribution is Lambertian.

It is often unsatisfactory, however, to utilize only a linear prism filmdirectly in a lighting application. One skilled in the art willrecognize that the distribution shown in FIG. 5 is not advantageous foruniform lighting of a planar surface due to excessive suppression ofnadir intensity, which will manifest as a dark spot on the illuminatedsurface. Many lighting designers will find that Illuminance at nadir issimply too low to achieve desirable illumination uniformity in manyapplications.

To achieve a desirable 1D batwing distribution from a 90-degree linearprism, extra diffusion of the light is usually needed due toover-suppression of the nadir with linear prisms alone. FIGS. 6A and 6Bplot the measured light intensity distributions at phi=90 degrees,perpendicular to the prism orientation, of a luminaire employing a prismfilm followed by an additional diffuser layer, with gentle and strongdiffusing strength respectively. In the phi=0 degree plane, parallel tothe prism orientation, these distributions are not batwing; they areapproximately Lambertian, and thus the distribution is a 1D batwingdistribution. The data suggest that an added diffuser modifies the 1Dbatwing distribution from a prism film and the outcome is much moresuitable for general lighting applications than prism films alone.

Many 1D and 2D batwing distributions exist in the art.

Batwing distributions are known in the art, and are usually createdusing specific focusing optics (e.g. lenses and/or reflectors), and/orspecific features in the geometry of a light source, such as lampplacement, and placement of internal or external baffles, louvers,openings, and placement of ordinary diffusers. Examples include USPatent Application Publication 20050201103 A1, US Patent ApplicationPublication 20130044476 A1, U.S. Pat. No. 4,218,727 A, U.S. Pat. No.5,105,345 A, U.S. Pat. No. 6,698,908 B2, U.S. Pat. No. 3,329,812, EPPublication 1925878 A1, U.S. Pat. No. 3,725,697, U.S. Pat. No.7,273,299, U.S. Pat. No. 5,149,191, EP Publication 2112426 A2. In manycases the focusing optics, baffles, etc., increase the cost of aluminaire. These designs are generally strongly dependent on theplacement of the light source, and generally require alignment of thereflectors, baffles, etc. with the light source. Designing theseluminaires with 1D or 2D circular or rectangular batwing distributionsis generally difficult and slow, requiring either advanced computermodeling or trial-and-error testing, which can be too costly for somesmaller lighting manufacturers. In particular, rectangular and squarebatwing distributions are the most difficult to create, due to the lackof a radial symmetry.

In U.S. Pat. No. 3,721,818, Stahlhut describes an article capable ofcontrolling light distributions, such as reducing glare and creating 1Dand 2D batwing distributions. The article involves shaped surfaces onone or both sides of a substrate, with additional “light reducing areas”(e.g. paint) which can be opaque, reflective or absorbing. Undesirably,the need for these light reducing areas may both increase cost anddecrease efficiency of the light fixture. In some embodiments, the needto create structures on both sides of the surface that are aligned toeach other may also add expense and complexity.

In U.S. Pat. No. 3,866,036, Taltavull describes a prism-like structureincluding prisms or linear lenses with truncated tips upon which thickopaque structures are formed. These may create effective batwing lightdistributions but may be expensive and difficult to create, and theopaque structures may incur additional losses of light, reducing overallfixture efficiency.

In addition, the lack of diffusion in these structures means that fromcertain viewing angles, the light source(s) may be visible asundesirable bright spots on the surface of the luminaire.

In U.S. Pat. No. 3,978,332, Taltavull describes a ring-shaped structureincluding concentric prisms or linear lenses with truncated tips uponwhich are created opaque structures. These can create effective 2Dbatwing light distributions but may be expensive and difficult tocreate, and the opaque structures may incur additional losses of light,reducing overall fixture efficiency. Taltavull additionally uses theexact placement of lenses and a carefully designed reflector, all ofwhich elements together combine to create the desired 2D batwing lightdistribution, which may add further expense.

In U.S. Pat. No. 4,161,015, Dey et. al., describe a luminaire withbatwing distribution created by selective reflectivity from a multilayerinterference filter with reflectivity and transmissivity that vary withangle of incidence. Unfortunately such an interference filter may beexpensive to create, and may generally be wavelength-sensitive. Inaddition, when viewed from certain angles, there is undesirably noobscuring of the light sources.

In US Patent Application Publication 20090296401 A1 Gutierrez describesa system that uses a moving resonant mirror to create a desired lightdistribution, including batwing distribution. Such a system may sufferfrom excess power consumption, noise created by the mechanical motion,flicker, and possibly reliability issues associated with moving parts.

In U.S. Pat. No. 4,059,755 A, Brabson describes the use of threedifferent prism optics in two layers to create a 1D batwingdistribution. This system may undesirably need to be aligned to a linearsource. Undesirably, the two layers of custom prism optics may beexpensive, and may incur a reduction of efficiency associated withreflections from multiple optical interfaces.

In many other examples, including US Patent Application Publication20090225543, US Patent Application Publication 20120275150, PCTPublication WO2012109141 A1, U.S. Pat. No. 7,658,513, US PatentApplication Publication 20130042510, U.S. Pat. No. 8,339,716 B2, USPatent Application Publication 20130039090 A1, U.S. Pat. No. 7,273,299B2, U.S. Pat. No. 7,731,395 B2, US Patent Application Publication2009096685 A2, US Patent Application Publication 20110141734 A1, U.S.Pat. No. 7,942,559 B2, U.S. Pat. No. 7,993,036 B2, individual lightsources (typically LEDs or collections of LEDs) are modified usinglenses, reflectors, light pipes, or the LED package, in close proximityto light sources. Many light distributions can be created this way (asknown in the art), including 1D and 2D batwing distributions. In manygeneral lighting applications, large numbers of LEDs (typically tens orhundreds) are used over the area of the luminaire, and the use of lensedLEDs with non-Lambertian distributions can be costly. Also, individualLEDs can be piercingly bright when unobscured, even if focused usinglocalized lenses. To achieve desirable smooth appearance of a luminaireand obscure the light sources, additional diffusers may be required,incurring higher costs. Further, such diffusers may in some cases not beable to sufficiently homogenize the surface appearance of the luminairewithout degrading the distribution created by the LEDs.

In U.S. Pat. No. 2,394,992, Franck describes a luminaire with 2Delliptical batwing light distribution employing a lamp (substantially apoint source) illuminating a compound lens with Fresnel-lens-like prismson both surfaces. One surface is a radial compound Fresnel lensincluding a central spreading region and a peripheral focusing region toform a 2D circular batwing distribution. The other surface is a linearFresnel lens which is the regressed optical equivalent of a negative ordivergent cylindrical lens surface and provides additional spreading ofthe batwing distribution along one axis, transforming the circularbatwing to an elliptical batwing distribution. This solution may dependon a light source that is substantially a point-source, and thus may notwork with extended Lambertian sources. In addition the optic undesirablyis custom designed for the luminaire (e.g. the distance from the lightsource and total illuminated diameter), and may need to be aligned tothe light source.

In U.S. Pat. No. 5,997,156 A, Perlo et. al. describe creatingrectangular or square light distributions using rippled lenticularlenses or TIR prism lenses in conjunction with a collimated light source(in the example provided, using a parabolic reflector). However, thetechniques mentioned may not work with Lambertian light sources.

In U.S. Pat. No. 3,829,680, Jones describes a lighting panel with acontinuous pattern of triangle projections, each triangle having threemutually perpendicular smooth faces (in today's nomenclature, such apattern is often called “corner cube”). This lighting panel can providea 2D batwing distribution from Lambertian light input. The distributioncreated by this type of structure has a hexagonal rosette pattern whenviewed on a flat floor (due to having refraction through repeated flatplanes at only six geometric orientations), and is a rough approximationto a 2D circular batwing distribution. In some cases, these hexagonalartifacts will be undesirable to lighting designers. In addition, due tothe small number of geometric orientations of the faces, light sourcesare not sufficiently obscured for many lighting purposes. Jonesdiscloses the use of a diffuser in conjunction with the corner cubesheet, which successfully obscures the light sources but incurs extraexpense and loss of efficiency associated with reflections from theextra optical interfaces involved in using two separate opticalelements.

In U.S. Pat. No. 586,211, Basquin describes a window composed of prismsthat are designed to spread sunlight into a room. Basquin arranges theprisms in unit cells (e.g. hexagons or squares), with prisms within eachunit cell having a desired orientation, the net effect of the prisms inall oriented cells having a desired effect on the light. Basquin isdesigned to work with sunlight, which will be recognized by thoseskilled in the art as a collimated light source relative to a window.Basquin does not create a 2D batwing light distribution.

In U.S. Pat. No. 4,984,144, a light fixture is provided in which a highaspect ratio fixture (such as a thin sign) is illuminated from the side,and in which prisms are used in total internal reflection (TIR) mode todirect light outside the fixture, maximizing light exiting at an anglenormal to the surface of the fixture (and thus not in a batwingdistribution). Because of the internal side illumination, the lightsource is strongly directional, and thus not Lambertian. This fixturedoes not produce a batwing distribution.

In U.S. Pat. No. 5,193,899, a prism is used in conjunction with adiffuser to increase the uniformity of brightness on the surface of asign to hide “lamp images” (i.e. provide a smooth appearance on thesurface of the sign) that obscures the location and visibility of theunderlying lamps. Because of the strong diffusers used to make thesurface of the sign highly uniform, the fixture does not emit light in abatwing distribution.

In U.S. Pat. No. 5,243,506 A, a light-pipe architecture illuminated by asingle source at the end of the light pipe uses prisms to couple lightout of the light pipe at a point and in a direction substantiallyperpendicular to the surface of the light pipe at that point. By usingmetal masking in selective locations to determine where light can strikethe prisms and escape the light pipe, 1D light distributions including1D batwing distributions can be sculpted.

CN 202532218 U discloses a lamp structure with batwing light intensitydistribution. The lamp structure comprises at least two light-emittingdiode (LED) groups, a light guide plate, a reflecting part and a prismsheet, and is characterized in that: the light guide plate is providedwith a first surface and a second surface; and the first surface isprovided with a micro structure. Distribution in a way that both sidesare sparse while middle is dense is adopted, so that the refractionangle of light rays is changed, and the light rays are refracted out ofthe light guide plate. Light rays are uniformly scattered effectivelythrough the geometric structure on the prism sheet facing the lightguide plate, so that batwing light intensity distribution is achieved.

Investigation

In trying to design an optical film or plate with 2D circular batwingdistribution, the present inventors considered surface featuresincluding close-packed arrays of cones, which is the 2D analog of a 1Dlinear prism. As mentioned earlier, it is known that when a prism opticis illuminated with Lambertian light impinging upon the smooth side(i.e., used in a brightness-enhancing orientation, rather than abatwing-generating orientation), the intensity is amplified at thenadir, while the FWHM is reduced. Analogously, when a close-packed conearray optic is illuminated by Lambertian light upon the smooth side, theintensity is amplified at the nadir, while the FWHM is reduced, as oneskilled in the art would expect, and as the 1D prism-2D cone analogywould imply. Also as expected, this light distribution substantially hasradial symmetry around the theta=0 axis.

In the opposite orientation, as mentioned earlier, Lambertian lightentering the prism side of a prism sheet (i.e., used in thebatwing-generating orientation) provides an approximate 1D (linear)batwing distribution. Expecting Lambertian light entering the cone sideof a cone sheet to analogously form a 2D circular batwing distribution,the present inventors tested a commercially-available sheet comprisingan array of cones protruding from one side, with a smooth surface on theopposite side. The cones were arranged in a hexagonal grid on a 2 mmrepeat length, with 100 degree internal angle at the tip. Surprisingly,upon testing, the cones did not create a batwing distribution at all, asshown in FIG. 7, measured using an incoming 120 degree Lambertiandistribution. When measured with an 80 degree Lambertian incoming lightdistribution, the cones again did not create a batwing distribution, asshown in FIG. 8. The same cone array was then tested with collimatedlight illuminating the cone side, and as expected, created a circle oflight. The slice measured at phi=0 is shown in FIG. 9, with slicesmeasured at any other azimuthal angle substantially the same. Similarly,the same cone array was measured with a near-collimated 20-degree lightinto the cone side, and created the batwing-like distribution of FIG.10. Thus a cone array can create batwing distributions for collimatedand narrow near-collimated distributions, while surprisingly failing todo so for wide (Lambertian) distributions.

Additional References

In US Patent Application Publication 20120275185, Edamitsu discloses anilluminator that creates 2D batwing distributions using prisms facingthe light source. In this publication, no detail is given as to theincoming light distribution produced by the light source (it is notstated whether the light source is collimated or Lambertian). However,the light distribution of the light source can be deduced from the dataprovided. In the embodiment of FIG. 5 of that '185 publication, it isstated that a cone array, with flat spaces in between, can produce abatwing distribution shown in FIG. 6 of the '185 publication. Inconsideration of the data provided on cone arrays by the presentinventors, one can determine that the data of FIG. 6 of the '185publication only makes sense if the source is substantially collimated.This is similarly true for the other embodiments in the '185publication. The addition of and need for flat areas, as described tofill in extra light at nadir, also implies a collimated light source.Such flat areas generally are necessary in part because of thecollimated light—without the flat areas, upon illumination by collimatedlight there would be substantially no illumination at nadir, providinginsufficient illumination at nadir to evenly illuminate a flat surface.Substantial flat areas are disadvantageous when used with Lambertianlight sources, however, because too much Lambertian light is passedthrough said flat areas, reducing or preventing batwing distributionsfrom being formed. In addition, flat areas in a lighting optic areparticularly disadvantageous because they allow a direct view of thelight sources (lamps), whereas hiding or obscuring lamps in lighting isgenerally preferred.

Similar to the '185 publication, US Patent Application Publication20130070478, Edamitsu discloses an approximate cone including ahexagonal prism, interspersed with triangular corner-cube elements. Asin the '185 publication, the '478 publication does not disclose thelight distribution of the light source used in testing, but it can bededuced to be substantially collimated following the same argumentabove. This approximate cone can be reasonably expected by one skilledin the art to have performance similar to a cone, which as shown by thepresent inventors' data above has limitations on its ability to formbatwing distributions from Lambertian light. In addition, the complexstructure is difficult to manufacture, generally requiring precisiondiamond cutting of a master form or tool. As with Jones' U.S. Pat. No.3,829,680, discussed above, the '489 publication describes planarsurfaces oriented in only six directions. Due to this small number ofgeometric orientations of the faces, light sources are not sufficientlyobscured for many lighting purposes.

Although in some cases the patterns of Edamitsu's '185 and '478publications, and Jones' 680 patent may achieve 2D batwing distributionthat are acceptable to some lighting designers and specifiers, thepatterns of various embodiments described herein may be particularlyadvantageous due to their ability to work with Lambertian sources,increased obscuration of light sources, ease of manufacture, smoothnessof light distribution, flexibility and controllability of the lightdistribution and its shape (such as making square or rectangulardistributions), and/or capability of creating visually pleasing surfacepatterns.

In U.S. Pat. No. 7,660,039, Santoro et al. disclose kinoform diffusersthat (a) reduce luminance at high viewing angles (known as glare),and/or (b) when disposed on either side of transparent or curved“centrally located regions” directly beneath light sources produces a 1Dor 2D batwing luminous intensity distribution. Undesirably, this“centrally located region” appears to be required to form a batwingdistribution. Of the embodiments employing a contiguous or monolithicdiffuser (and thus having no curved or transparent “centrally locatedregion”), none provide a batwing luminous distribution (although many ofthem reduce glare). When a “centrally located region” is included andlocated directly below the light source as taught, then rays emitteddownward and near-downward by the light source toward said region do notstrike the kinoform diffuser, which is located at the sides. Thus thekinoform diffuser itself is not creating a batwing distribution from aLambertian light source. Rather two spatially-separated kinoformdiffusers (neither of which is directly beneath the light source)cooperate to create a batwing distribution (creating one half of thedistribution each) from collections of rays that are directional (eachhaving a strong sideways component) and contain substantially nodirectly-downward component to their direction, and thus are notLambertian. The need for a “centrally located region” may increaseexpense, and, in the embodiments for which said region is transparent,there is undesirably no obscuration or hiding of the lamps.Additionally, the diffuser may need to include multiple light scatteringelements, “on each of which are one or more sub-elements.” In practicethese sub-elements may be very difficult to create and control.Advantageously, various embodiments described herein do not requirekinoform or holographic diffusers, do not require such sub-elements, andcan be used in contiguous spans without the need for transparent orcurved “centrally located regions.”

In U.S. Pat. No. 7,837,361, Santoro et al. disclose a light controldevice implemented with a diffuser that creates batwing light intensitydistributions. As with the Santoro '039 patent, a “centrally locatedregion” appears to be required to form a batwing distribution, resultingin the same disadvantages explained above for the '039 patent.

In U.S. Pat. No. 8,047,673, Santoro describes a light control deviceimplemented with multiple diffusers. The light control devices andluminaires disclosed create 1D batwing light distributions by means of acentral lamp, multiple diffusers, and openings with carefully designedplacement. As described above, the placement of the diffusers separatedby a central element means that each diffuser receives light from anon-Lambertian collection of rays and does not create a batwing lightdistribution from a Lambertian light distribution. The luminairedescribed does create 1D batwing distributions, but does so using thediffusers, lamp, openings, and internal reflections workingcollectively, and thus is distinct from various embodiments describedherein, which can create 2D batwing distributions from Lambertian light.

Potential Advantages

Various embodiments described herein can provide a 2D batwing diffuserthat can form light into useful 2D batwing distributions, including butnot limited to elliptical, circular, rectangular, and squaredistributions.

Various embodiments described herein can provide a 2D batwing diffuserthat can, when used in a luminaire, provide substantially uniformillumination over a flat surface of a defined shape, including but notlimited to elliptical, circular, rectangular, and square shapes.

Various embodiments described herein can provide a 2D batwing diffuserthat can form light from Lambertian-distributed sources, including LEDpoint sources and LED arrays, into useful 2D batwing or flat-fielddistributions.

Various embodiments described herein can provide a 2D batwing diffuserthat can form light from approximately-Lambertian sources into useful 2Dbatwing or flat-field distributions.

Various embodiments described herein can provide a 2D batwing diffuserthat can form light from substantially collimated or near-collimatedsources into useful 2D batwing or flat-field distributions.

Various embodiments described herein can provide a contiguous ormonolithic 2D batwing diffuser that can form 2D batwing distributionswithout requiring cooperation from other light emitting region(s) suchas a centrally located transparent region.

Various embodiments described herein can provide a 2D batwing diffuseroptic for a luminaire that does not require specific alignment relativeto the luminaire's light sources.

Various embodiments described herein can provide a 2D batwing diffuserthat is shift-invariant, and thus can be manufactured in large areassuch that a diffuser suitable for a given luminaire can be cut from anarbitrary location of the large area without the need to align the cutto specific optical features (such as a central point) of the opticalstructure.

Various embodiments described herein can provide a 2D batwing diffuserwith high optical transmission, having substantially no light-absorbingmaterials.

Various embodiments described herein can provide a 2D batwing diffuserthat obscures or helps obscure light sources, including but not limitedto LEDs and fluorescent lamps.

Various embodiments described herein can provide a 2D batwing diffuserthat increases the luminance uniformity on the surface of a luminaire.

Various embodiments described herein can provide a 2D batwing diffuserthat has a visible surface pattern that may be aesthetically pleasing toa viewer. Further, various embodiments described herein can provide a 2Dbatwing diffuser optic that has a visible surface pattern that visuallyobscures light sources such as LEDs, or distracts the eye to reducetheir visibility.

Various embodiments described herein can provide a 2D batwing diffuserthan can be efficiently and inexpensively mass-produced in areas largeenough to be suitable for use in general lighting.

Various embodiments described herein can provide a 2D batwing diffuserthat reduces luminance at high viewing angles relative to a Lambertiansource.

Various embodiments described herein can provide a substantially flat orslightly curved 2D batwing diffuser optic that can form light intouseful 2D batwing distributions.

Various embodiments described herein can provide 2D batwing diffuserthat when used with an appropriately configured specular reflector willcreate a one-sided distribution suitable for applications includingwall-wash and/or cove lighting.

Various embodiments described herein can provide a luminaire employing a2D batwing diffuser, the luminaire emitting light into a 2D batwingdistribution.

Various embodiments described herein can provide a luminaire employing a2D batwing diffuser optic, the luminaire emitting light into a one-sideddistribution suitable for wall-wash and/or cove lighting applications.

General Description

Various embodiments described herein can provide a 2D batwing diffusercomprising a substrate having a first and second surface, the firstsurface having pattern elements comprising a plurality of substantiallyparallel, approximately linear prismatic microstructures, or prisms,said prisms having multiple orientations within the array, configured tomodify the light distribution of a typical artificial light source intoa 2D batwing distribution. The prisms are substantially isoscelestriangular in cross-section, and may include other features such as arounded tip and/or valley, or surface roughness. In many embodiments,the prisms are curved, and in many embodiments, some or most of theprisms form closed, concentric geometric shapes.

Various embodiments described herein are based on the insight, after thesurprising failure of cone array optics to form batwing distributions,that arrays of parallel prisms having the indicated characteristics canform 2D batwing distributions from Lambertian light. In many embodimentsdisclosed herein, the 2D batwing diffuser does not require alignment tothe light source, and can be manufactured in large areas, with parts cutto size in substantially any layout.

Detailed Description of Embodiments

Prism-like structures can be ananged on a substrate S as illustrated inFIG. 11. The prisms are created on the surface of a substrate thatdefines the x-y axis, and thus the line defined by their peak is alwaysparallel to the x-y plane as defined in the figure. We choose to definethe orientation of a prism to be in the x-y plane and parallel to theline making the crest of the prism. The prism orientation angle is theangle measured in the plane from the x axis, counter-clockwise to theprism axis. The prism 2 has a prism orientation angle of roughly 0degrees from the x-axis, while the prism 4 has a prism orientation angleα of roughly 45 degrees from the x-axis. For a symmetrical prism, aprism orientation angle of 180 degrees is indistinguishable from a prismorientation angle of 0 degrees.

In FIG. 12, a curved prism 6 is presented. The peak of the prism forms acurved line that, once again, is substantially parallel to the plane ofthe substrate S (the x-y plane). This prism does not have oneorientation angle, but has a continuum of orientation angles rangingfrom 0 to 90 degrees. This curved prism can be approximated as thecombination of several shorter, substantially straight sub-prisms, eachat its own prism orientation angle. Similarly, a curved prism that madea complete circle would represent all prism orientation angles in equalmeasure. Section A-A shows a cross section upon which two features aredefined, (i) the prism pitch being the distance between the valleys oneither side of a prism peak, and (ii) the prism internal angle β, beingthe full angle subtended by the prism peak.

In some embodiments, a 2D batwing diffuser includes prisms arranged inpattern elements 10 having a plurality of concentric circles, as shownin FIG. 13, said circles of concentric and substantially parallel prisms12 arrayed upon the substrate in a desired pattern, such as close-packedhexagons.

In one particular example of the embodiment above, the prisms have 60micron pitch, and are repeated in a hexagonal array with dimension 250um to fill the surface of the diffuser. The prism internal angle isabout 90 degrees, and the refractive index is 1.49. When illuminatedwith 120 degree Lambertian light, this 2D batwing diffuser produces anapproximately radially-symmetric 2D batwing light distribution, as shownin FIG. 14. When illuminated with 40-degree Lambertian light, this 2Dbatwing diffuser produces an approximately radially-symmetric 2D batwinglight distribution that is narrower and has a greater degree of nadirsuppression, as shown in FIG. 15.

In an additional embodiment, the substantially parallel prisms arearranged in concentric circles and have 60 micron pitch in patternelements that are repeated in a hexagonal array with dimension 2.5 mm tofill the surface of the diffuser. The prism internal angle issubstantially 70 degrees, and the refractive index is 1.49. Whenilluminated with 40-degree Lambertian light, this 2D batwing diffuserproduces an approximately radially-symmetric 2D batwing lightdistribution shown in FIG. 16.

In an additional embodiment, a 2D batwing diffuser is created usingprisms arranged in a concentric circle pattern. The prisms have a pitchof 60 microns and repeated in a hexagonal array with dimension 4millimeters, creating a 2D circular batwing light distribution whenilluminated upon the prism side by Lambertian light. One unexpectedbenefit is that the hexagons are visible to the naked eye, and the arrayof hexagonal elements produces a pleasing surface pattern that addsartistic and visual appeal.

The geometric arrangement of prisms and the prisms' internal angles canbe changed in a multitude of ways to customize the light distributioncreated by a light source.

In the embodiment of FIG. 17, the prisms 14 take the shape of asquared-off circle (examples include but are not limited to thegeometric shapes known as squircle and superellipse), arrayedsubstantially parallel to one another in concentric diamond-shaped (i.e.45-degree tilted square) pattern elements 16. As depicted in FIG. 17,there exists a greater area on the substrate covered by prisms orientednear 45 and 135 degrees, and a reduced area on the substrate covered byprisms oriented near 0 and 90 degrees relative to the x axis indicatedin the figure. In this embodiment, in any representative area comprisingseveral elements, all prism orientation angles are represented, withprism orientation angles near 45 and 135 degrees being represented bymore area on the substrate than prisms near 0 and 90 degrees. Whenilluminated by Lambertian illumination, this diffuser will produce a 2Dbatwing light distribution that is somewhat square, and brighter near 45and 135 degrees and less bright near 0 and 90 degrees.

In the embodiment of FIG. 18, the prisms of FIG. 17 have been furthermodified to create a substantially 2D square batwing distribution. Inaddition to the same somewhat-square footprint of the embodiment of FIG.17, the prisms' 14′ internal angle is varied as a function of the prismorientation angle. As indicated in the figure, the prisms that areoriented near 45 degrees (indicated by Section A-A) and 135 degrees havea smaller internal angle β than the prisms oriented near 0 degrees(indicated by Section B-B) and 90 degrees. The smaller prism angleresults in steeper prism sidewalls, giving a wider light distributionalong the 45 and 135 degree orientations. This wider distributioncoupled with the higher light intensity created by the relatively higherproportion of the substrate area covered by prisms with orientation near45 and 135 degrees leads to a light distribution that provides enhancedbrightness uniformity on flat surfaces over an approximately squarearea. When illuminated by a 40 degree Lambertian source, this diffuserproduces the light distribution shown in FIG. 19A. In FIG. 19A the solidline represents the light distribution measured with an angle phi=0,while the dashed line represents the light distribution measured atangle phi=45 degrees, along the diagonal of the square. As expected fora square-like distribution, the distribution is wider at phi=45 degreesthan at phi=0 degrees. FIG. 19B is a contour plot of the illumination ona flat surface caused by this light distribution, and the square natureof the illumination pattern can be seen. The scale on the horizontal (x)and vertical (y) axes is the offset on a flat surface such as a floorrelative to the mounting height of the luminaire over the floor. Thusfor a luminaire 10 feet above a floor, the points at x=1 on the plotrepresent a distance measured 10 feet away from nadir in the xdirection. When illuminated by an 80-degree Lambertian source, the 2Dbatwing diffuser of the embodiment of FIG. 18 produces the lightdistribution shown in FIG. 20.

In another embodiment (not pictured), elongation of the square prisms ofthe embodiment of FIG. 18 into a (non-square) rounded rhombus-likeshape, with appropriate changes to the prism curvatures and internalangle modulation results in a light distribution with uniformillumination over a rectangular (rather than square) area.

In another embodiment (not pictured), modification of the circularprisms of the embodiment of FIG. 13 into an (non-circular) ellipse, withthe addition of appropriate internal angle modulation will result in alight distribution with uniform illumination over an elliptical (ratherthan circular) area.

In another embodiment, the concentric circular prisms of FIG. 13 arepacked in a diamond- or square-shaped elements, similar to the shape ofthe elements 16 of FIG. 17.

In some embodiments, gaps may be present between at least some of themicroprism elements and gap-filling microstructures may be in at leastsome of the gaps. See, for example, the gaps 18 and gap-fillingmicrostructures 20 in FIGS. 13 and 17.

In many embodiments, periodic or non-periodic tilings (or tessilations)are used to arrange elements comprising concentric prisms. In someembodiments, the tiling may involve multiple tile shapes, such as in thecase of penrose tiling. In all cases, the light distribution achieved bya given luminaire employing a 2D batwing diffuser will be the sum of thelight distributions created by each of the elements comprising theentire 2D batwing diffuser of that luminaire.

In some embodiments, tiling is not used at all. In the embodiment ofFIG. 21, a 2D batwing diffuser comprises prisms made with random shapeand having variation in internal angle. A shape such as this can begenerated mathematically in many ways, for example by mathematicallygenerating a random bumpy data surface, and forming prisms along contourlines representing the height of the data surface. Because this random2D batwing diffuser still comprises prisms at all orientation angles andin equal measure, this diffuser will create a 2D batwing lightdistribution. This embodiment may offer advantages in surface appearanceand reducing the visibility (better scrambling) of the light sources toa viewer of the luminaire.

The characteristic size of pattern elements for a tiled arrangement ofpattern elements can be defined as the distance between each tile, oraverage distance between nearest-neighbor tiles in the case ofnon-periodic or irregular tilings.

Although it may be difficult to clearly define individual elements inthe embodiment of FIG. 21, the collection of concentric shapes could becalled “pseudo-elements” and still can be said to have a characteristicsize. The prism array shown has several locations that are relativemaxima or minima, having the maxima or minima of the random bumpsinvolved in generating the data surface as explained above. Thecharacteristic size of the pseudo-elements is simply the averagedistance between these maxima or minima of the data surface, which canbe determined by one skilled in the art through techniques such asFourier analysis. Thus the features in the embodiment of FIG. 21 canstill be said to have a defined characteristic size.

In another embodiment, the 2D batwing diffuser of FIG. 22 is created ina similar manner to the embodiment of FIG. 21, further modifying theshape to be asymmetric, having prisms that are on average longer alongone dimension than along the perpendicular dimension. This diffuser willhave an elongated distribution due to the increased concentration ofprisms with orientation near y axis compared to the concentration ofprisms oriented near the x axis.

In another embodiment (not pictured), the 2D batwing diffuser of FIG. 22is further modified to have prism internal angles which are modifiedfrom one location to another, to more effectively create an elongatedlight distribution.

Random distributions such in the above embodiments can be made to createsquare, rectangular, circular, or elliptical 2D batwing distributionsthrough combinations of geometric shape, local changes in internalangle, etc.

Sizes for Prisms and Elements

The characteristic size of the pattern elements (which, for example, inthe case of close-packed hexagons is the spacing between hexagons) willaffect various embodiments described herein as follows: If thecharacteristic size is very small (smaller than about 1 mm) it will beundetectable by the naked eye of an observer, and the surface of thediffuser will have a smooth appearance, which is desirable in somecases. If the characteristic size is larger than about 1 mm, it willpresent a visible pattern to the observer.

According to laboratory experiments by the applicants, pattern elementswith characteristic sizes large enough to produce visible patternsproduce an unexpectedly pleasing visual appearance, adding aestheticappeal to a luminaire in which it is used. An additional unexpectedbenefit of characteristic sizes large enough to produce visible patternsis that in laboratory observations, they were found to confuse the eye,giving the illusion of better hiding or scrambling of images of lightsources. Such visible surface patterns are particularly effective withLEDs, in scrambling light into pleasing patterns, and in the case whereadditional diffusion is used, increase the effectiveness of diffusers inhiding the LEDs. In some cases involving luminaires with arrays of LEDs,it may be desirable that the pattern elements be on a similar size scaleto the spacing between LEDs, in which case they provide the strongestscrambling or obfuscation of the visibility of LED sources.

If the characteristic size of the pattern elements is more than an orderof magnitude and in some embodiments, more than two orders of magnitude,and in some other embodiments, at least four orders of magnitude smallerthan the light exit surface of the luminaire, then the diffuser'sresponse to light will be substantially uniform over dimensionscomparable to said light exit surface of the luminaire. As such, thelight distribution created by the luminaire will not be sensitive to theexact placement of the diffuser in the luminaire. This is potentiallyadvantageous for allowing tolerance in the assembly of the luminaire,and additionally potentially advantageous in allowing the product to bemanufactured in sheets with large surface areas, from which 2D batwingdiffusers can be cut from any location on the sheet without needing toalign the cut to specific features on the 2D batwing diffuser pattern,saving cost. Thus in many cases it may be particularly advantageous thatthe characteristic size of pattern elements is more than an order ofmagnitude smaller, and in some embodiments more than two orders ofmagnitude smaller, and in some other embodiments at least four orders ofmagnitude smaller than the light exit surface of the luminaire in whichit is employed. A typical small size for the light exit surface of aluminaire is about 50 mm circular, and a typical large size for thelight exit surface of a luminaire is about a 1200 mm×600 mm rectangle.

In many of the embodiments, the characteristic size of pattern elementsis at least one or two or four orders of magnitude smaller than theluminaire in which it is employed. When this is true, the macroscopicoptical structure is substantially uniform on the size scale of theluminaire, and to a viewer would have a consistent surface appearance,be it a smooth texture (in the case when the characteristic size is verysmall) or a substantially uniform pattern (for larger, more visiblecharacteristic sizes). One can choose area on the surface of thesubstrate of a 2D batwing diffuser that encompasses several patternelements, or is several times the characteristic size of patternelements, as illustrated in FIG. 23. This area is will to contain prismswith a distribution of prism orientation angles according to the designof this particular 2D batwing diffuser, and light illuminating that areawill be affected by the prisms in accordance with the prism orientationangles found in that area of the substrate. For example, if an area ofthe substrate contains prisms with prism orientation angles of 0 degreesand 90 degrees in equal proportion, then upon illumination the lightdistribution will be the sum of the light distributions created by 0degree and 90 degree prisms, in the same proportion. If one such areacontains prisms with 0 degree prism orientation angle within 75% of itsarea on the substrate, and prisms with 90 degree prism orientation anglewithin 25% of its area on the substrate, then the light distribution bethe sum of the light distributions created by 0 degree and 90 degreeprisms, in the same 75%/25% proportion. Now it is possible to choose asecond area of similar size in a different location of the surface ofthe 2D batwing diffuser that contains a group of prisms withsubstantially the same distribution of prism orientation angles, andhave substantially the same response to incoming light. By extension, itis possible to choose areas covering the entire substrate and havingsubstantially the same distribution of prism orientation angles. Giventhe similarity of these chosen areas, the 2D batwing diffuser issubstantially uniform over the spatial size of the substrate. For casesin which a continuous group of prism orientation angles is represented(such as a curved prism), the prisms can be represented as a sum ofsmall straight prisms, each with a defined prism orientation angle, andthe light distribution will similarly be a sum of a the lightdistributions created by the constituent sub-prisms. It can also bethought of as a sum of light distributions at each orientation angle inproportion to the surface area on the substrate occupied by prisms ateach corresponding prism orientation angle.

Due to the preference that the characteristic size of pattern elementsis significantly smaller than the size of the luminaire, and that thepattern elements are composed of a plurality of substantially parallelprisms and thus the individual prisms have a pitch that is generallysmaller than the characteristic size of pattern elements, the prismswill in many embodiments be quite small, often smaller than 1 mm, andsometimes smaller than 100 microns. In these cases the individual prismsmay be desirably invisible to the naked eye, while the pattern elementsmay be large enough to be desirably visible. However it is not strictlynecessary that the prisms be this small. In some embodiments, the prismsmay be visible to the naked eye. In one example embodiment, patternelements are close hexagonally-packed regions of 50 mm size in whichprisms with 2 mm pitch are arranged pattern in concentric circles, andthe regions are repeated over a panel 600×1200 mm in size.

FIG. 24 shows typical order-of-magnitude sizes in meters for the prismpitch (labeled “Prism”), the characteristic size of pattern elements(labeled “Pattern Element”), and luminaires employing 2D batwingdiffusers (labeled “Luminaire”). These are only typical values, and donot place upper or lower limits on the sizes of any features of theembodiments described herein.

If the characteristic size of the pattern elements is approximatelyequal to or larger than the size of the light exit window of theluminaire, the 2D batwing diffuser will comprise substantially onepattern element. An example of a 2D batwing diffuser composed of asingle element containing concentric circular prisms is shown in FIG.25A. In laboratory experiments, the applicants have found bothadvantages and disadvantages to this approach.

At the time of the experiments, a large 2D batwing circular prismdiffuser suitable for testing on a luminaire was not available. Theapplicants created a multi-prism plate approximating 2D batwing circularprism diffuser by piecing together portions of a 1D linear prism film,in eight triangular “pie wedges” as shown in FIG. 25B, with the prismsbeing oriented substantially parallel to the circumference of the shape,as depicted by the lines in the figure. Such a diffuser would appearsimilar to a Fresnel lens, although it is specifically composed prismsof isosceles triangular cross-section. It does not provide focusing orimaging performance, and it does not have any vertical sidewalls, bothof which are characteristic of a Fresnel lens. The size of the diffuserwas approximately 12 inches in diameter, comprised of prisms with 90degree internal angle and approximately 25 micron pitch, and it wastested on a 4-inch circular LED luminaire, the extra surface area beingunnecessary, but helpful in facilitating the tests below. The prismsfaced toward the light source in the testing.

This approximately circular array of prisms, combined with additionaldiffusion, modifies a Lambertian light distribution approximately into acircular 2D batwing distribution. FIG. 26 plots measured output of theLED luminaire passed first through this prism array, with the prism sidefacing the light source, and then through a gentle (15 degree FWHM)diffuser. This result demonstrates the feasibility of creating a 2Dcircular batwing distribution from a typical light source using a singlelarge pattern element. In above experiment, the multi-prism plate iscentered upon the round downlight aperture, as shown in FIG. 27A.

In a second experiment, the multi-prism plate was purposely misalignedfrom the center of the luminaire's light exit region, as shown in FIG.27B. FIG. 28 shows the resulting measured luminous intensitydistribution, which has become asymmetric. Like this multi-prism plate,a true concentric circular prism array would create a circular (andsymmetric) 2D batwing distribution when aligned substantially to thecenter of the light source, and could be used to create other usefuldistributions, including a one-sided batwing distribution, when alignedto points not centered on the light source.

In other embodiments, a 2D batwing diffuser is created using anarrangement of straight (linear) prisms shown in FIG. 29 on one side ofa translucent substrate. Prisms with pitch of 100 microns are arrayed inelements (in this case squares) 1400 microns in size, in two alternatingprism orientation angles, 0 and 90 degrees. In any small representativearea of about 1 square inch in size, the proportion of prisms at 0 and90 degrees is approximately equal. Upon illumination, the lightdistribution of such a 2D batwing diffuser is the sum of the lightdistributions of linear 1D prisms oriented at 0 and 90 degrees,respectively. On spatial scales ranging from several inches to severalfeet, the 2D batwing diffuser appears approximately uniform.

In other embodiments, a 2D batwing diffuser is created using anarrangement of straight (linear) prisms shown in FIG. 30 on one side ofa translucent substrate. Prisms with pitch of 200 microns are arrayed inelements (in this case squares) 2800 microns in size, in four prismorientation angles, 0, 45, 90, and 135 degrees. In a representative areaof about 1 square inch in size, all four of these angles are representedin substantially equal proportion. Upon illumination, the lightdistribution of such a 2D batwing diffuser is the sum of the lightdistributions of linear 1D prisms, and approximates a radially-symmetric2D batwing distribution.

In other embodiments, a 2D batwing diffuser is created using anarrangement of straight (linear) prisms on one side of a translucentsubstrate. Prisms with pitch of 100 microns are arrayed in elements 1400microns in size. Within each element, the linear prisms have prismorientation angles that are random (that is, any angle between 0 and 180degrees).

In a representative area 1 square inch in size, a random set of prismorientation angles is represented that is approximately uniform over allangles. Upon illumination by a 40-degree Lambertian light source, thelight distribution of such a 2D batwing diffuser is the sum of the lightdistributions of the constituent linear 1D prisms, and approximates aradially-symmetric 2D batwing distribution, as shown in FIG. 31.

In additional embodiments, a luminaire is provided which uses any of the2D batwing diffusers of the embodiments above to create a luminaire witha 2D batwing distribution.

In other embodiments, a round luminaire as illustrated in FIG. 32 isprovided with a light source, internal diffuse reflector, and 2D batwingdiffuser according to the embodiments above. The luminaire produces a 2Dbatwing distribution.

Note that the 2D batwing distribution is produced by the prism structureof the diffuser, and is not necessarily related to either the shape ofthe substrate or the shape of the output surface of the luminaire. Thusa luminaire with a light emitting surface that is circular in shapecould be made to produce a 2D batwing distribution on a flat surfacethat is circular, elliptical, square, rectangular, or other shape.

In other embodiments, a round luminaire as illustrated in FIG. 33 isprovided with a light source, internal specular reflector, and 2Dbatwing diffuser according to the embodiments above. The specularreflector is shaped in a substantially truncated conical shape. Theluminaire produces a 2D batwing distribution.

In other embodiments, a round luminaire as illustrated in FIG. 34 isprovided with a light source, internal specular reflector, and 2Dbatwing diffuser according to the embodiments above. The specularreflector is shaped in a curved shape such as an ellipsoid orparaboloid. The luminaire produces a 2D batwing distribution.

In other embodiments, a rectangular luminaire as illustrated in FIG. 35is provided with an array of light sources, internal reflector, and 2Dbatwing diffuser according to the embodiments above. The luminaireproduces a 2D batwing distribution.

In other embodiments, a rectangular luminaire as illustrated in FIG. 36has a diffuser with center section 22 surrounded by an outer section 23.The luminaire is provided with a light source or array of light sources21 located above the central section 22 and a 2D batwing diffuseraccording to the embodiments above in the center section 22 with prismsfacing toward the light source 21, and a conventional diffuser withlight to moderate diffusion (such as 20-degree FWHM) in the outersection 23. The luminaire is provided with a specular or diffusereflector (not shown) closing the cavity between the light source anddiffuser to enhance efficiency. The luminaire produces a 2D batwingdistribution and reduces luminance at high angles. In another variationof these embodiments, the center section has a shape other than a squareas indicated, such as a circle. In another variation of theseembodiments, both the conventional diffuser and the 2D batwing diffuserare formed on the same substrate, the conventional diffuser not coveringthe area covered by the 2D batwing diffuser. In another variation ofthese embodiments, the conventional diffuser and the 2D batwing diffuserare formed on the same substrate, the conventional diffuser covering theentire surface of the substrate facing away from the light source, andthe 2D batwing diffuser covering the center portion of the surface ofthe substrate facing the light source such that the center portion hasboth 2D batwing diffuser and the conventional diffuser on opposing sidesof the substrate.

In other embodiments, a 2D batwing diffuser is suspended below a lightsource, with open gaps beside the light source, such that lighttransmitted through the 2D batwing diffuser is directed downward in a 2Dbatwing distribution, and light reflected from the diffuser continuesupward to illuminate a ceiling, as shown in FIG. 37. The diffuser can besuspended under the light source via any techniques known in the art(not shown) including cables, a frame at sides or edges, or transparentenclosure. In variations of these embodiments, additional elements suchas 2D batwing diffusers, conventional diffusers, baffles and louvers areused to further shape the upward directed light into a batwingdistribution.

In additional embodiments, other types of luminaires known in the artcan employ a 2D batwing diffuser according to any of the embodimentsdescribed herein and produce a 2D batwing distribution, said luminairesincluding but not limited to downlight, recessed troffer, surface-mounttroffer, suspended pendant, suspended linear pendant, wall wash, cove,replacement lamp, PAR lamp, architectural, fine art, outdoor, bollard,aisle, stage/show lighting, movie lighting.

In additional embodiments, luminaires including a 2D batwing diffuseraccording to any of the embodiments described herein may employadditional elements such as conventional diffusers, additional 2Dbatwing diffusers, linear batwing diffusers, baffles, louvers, specularreflectors, diffuse reflectors, absorbers, openings, to further modifythe light distribution for purposes such as obscuring lamps, enhancingor de-emphasizing nadir suppression, reducing high-angle luminance(glare), or forming asymmetric or one-sided distributions.

In additional embodiments, one or more specular reflector is used inconjunction with a light source and 2D batwing diffuser according to anyof the embodiments described herein, to reflect or “fold” a 2D batwingdiffuser, creating a one-sided asymmetrical 2D batwing distribution. Anexample of this type of reflected design is shown in FIG. 38.

Luminaires are known in the art that collect outdoor light (i.e. directand/or diffuse solar light) and transmit the light to a desiredlocation, often diffusing the light at that location using aconventional diffuser or other light-transmitting material. Acommercially-available example is Solatube, of Vista, Calif.(http://www.solatube.com). In additional embodiments described herein, aluminaire including a solar collector, a light-transmitting member suchas tube with reflective inner walls or fiber optic cable assembly, and alight-exiting surface, through which light is emitted into a space andonto a flat surface is provided with a 2D batwing diffuser according toany of the embodiments described herein, and emits light into a 2Dbatwing distribution, as illustrated in FIG. 39. In additionalembodiments, a 2D batwing diffuser according to any of the embodimentsdescribed herein is used with a collimated or near-collimated incominglight distribution, creating a 2D batwing distribution.

The use of an appropriate diffuser with a collimated or near-collimatedlight source can widen the light source into a Lambertian light source.For example, it is known in the art that opal glass will transformnearly any incoming light distribution into an approximately 120-degeeLambertian distribution. In an additional example, it is known in theart that a conventional 60-degree diffuser will transform a collimatedsource into an approximately 60-degree Lambertian distribution. Thus a2D batwing diffuser with a collimated or near-collimated light sourceand an appropriate level of diffusion will perform similarly a 2Dbatwing diffuser with a Lambertian incoming light distribution.

In additional embodiments, a 2D batwing diffuser according to any of theembodiments described herein is used with a collimated ornear-collimated incoming light distribution and a conventional diffuser,creating a 2D batwing distribution.

In additional embodiments, a 2D square batwing diffuser according to anyof the embodiments described herein is illuminated by a 5-degreesubstantially-collimated incoming light distribution and results in thesqure 2D batwing distribution shown in FIG. 40, the solid linerepresenting the measurement at phi=0 degrees and the dashed linerepresenting measurement at phi=45 degrees. The degree of nadirsuppression achieved in this case is greater than the ideal forilluminating a flat surface, but may be desirable for certainillumination tasks. There is also an unintentional increase in lightnear nadir, visible as an additional bump in the center of FIG. 40,which is an artifact of the manufacturing process used to make thediffuser of this embodiment. It likely results from unintentional flatsurfaces in the microprism layer. Such an artifact may or may not bedesirable, and may be included or removed by appropriate modification ofthe manufacturing process.

In additional embodiments, a 2D batwing diffuser according to any of theembodiments described herein with included diffusion (such as surfaceroughness, rounding of prism peaks and/or valleys, curved surfaces, adiffusive substrate, or a diffusive second surface) is used with acollimated or near-collimated incoming light distribution, creating a 2Dbatwing distribution.

In additional embodiments, a 2D batwing diffuser according to any of theembodiments described herein with included surface roughness asillustrated in FIG. 41 is used to create a 2D batwing distribution.

In additional embodiments, a 2D batwing diffuser according to any of theembodiments described herein designed to produce a 2D square batwinglight distribution when illuminated by a 50 degree Lambertian incominglight distribution is used with a near-collimated 20-degreedistribution, and results in a 2D batwing distribution with more nadirsuppression than ideal for illuminating a flat surface, as shown in FIG.42A, in which the solid line represents the measurement at phi=0 and thedashed line represents the measurement at phi=45 degrees. In relatedembodiments, a second 2D batwing diffuser according to any of theembodiments described herein is created with substantially the samedesign, but with the addition of surface roughness comprising randombumps that are approximately the same width as the prism pitch, andapproximately ¼^(th) of the height of the prisms. This added surfaceroughness adds diffusion, reducing the nadir suppression as shown inFIG. 42B to a more desirable level for illuminating a flat surface. Inaddition, the added surface roughness provides better obscuration of thelight sources than embodiment without the surface roughness.

In an additional method, a flat surface is illuminated uniformly by aluminaire with a 2D batwing distribution employing the 2D batwingdiffuser of any of the above embodiments.

Manufacturing

The 2D batwing diffusers according to any of the embodiments describedherein can be created using many techniques known in the art.

The shape of the prisms may be cast onto a substrate using a suitablemaster mold, and thermally-curing polymer or ultraviolet (UV) lightcuring polymer, or the shape may be impressed into a thermoplasticsubstrate through compression molding or other molding, or may becreated at the same time as the substrate using extrusion-embossing orinjection molding.

The microstructures may be produced by replicating a master, asillustrated at Block 34 of FIG. 43. For example, an optical diffuser canbe made by replication of a master containing the desired shapes asdescribed in U.S. Pat. No. 7,190,387 B2 to Rinehart et al., entitledSystems And Methods for Fabricating Optical Microstructures Using aCylindrical Platform and a Rastered Radiation Beam; U.S. Pat. No.7,867,695 B2 to Freese et al., entitled Methods for MasteringMicrostructures Through a Substrate Using Negative Photoresist; and/orU.S. Pat. No. 7,192,692 B2 to Wood et al., entitled Methods forFabricating Microstructures by Imaging a Radiation Sensitive LayerSandwiched Between Outer Layers, assigned to the assignee of the presentinvention, the disclosures of all of which are incorporated herein byreference in their entirety as if set forth fully herein. The mastersthemselves may be fabricated using laser scanning techniques describedin these patents, and may also be replicated to provide diffusers usingreplicating techniques described in these patents.

In other methods and systems, laser holography, known in the art, isused to create a holographic pattern that creates the desiredmicrostructure in a photosensitive material.

In other methods and systems, projection or contact photolithography,such as used in semiconductor, display, circuit board, and other commontechnologies known in the art, is used to expose the microstructuresinto a photosensitive material.

In other systems/methods, laser ablation, either using a mask or using afocused and modulated laser beam, is used to create the microstructuresincluding the indicia in a material.

In other methods and systems, micromachining (also known as diamondmachining), known in the art, is used to create the desiredmicrostructure from a solid material.

In other methods and systems, additive manufacturing (also known as 3Dprinting), known in the art, is used to create the desiredmicrostructure in a solid material.

Variations

Many other variations on the structure may be provided according tovarious embodiments described herein.

The substrate may be thin, such as a flexible plastic film, or thick,such as a rigid acrylic or polycarbonate sheet. It may be monolithic orinclude multiple layers, such as a thin plastic film laminated to athicker rigid substrate using an adhesive layer or other laminationmethod. The diffuser may be substantially flat, or may take on acurvature (concave or convex; cylinder-like or dome-like) as long as thediffuser still forms a 2D batwing distribution. Additional optical ormechanical layers may be present, such as a cladding layer of differingrefractive index disposed outside of the 2D batwing diffuser prismlayer.

2D batwing diffusers according to any of the embodiments describedherein are designed to accept a light distribution provided by aluminaire's light source and components excluding the 2D batwingdiffuser (the “incoming light distribution”) and create a useful 2Dbatwing distribution of a desired shape. In some cases, the incominglight distribution will be Lambertian with 120 degree FWHM. In othercases, the incoming light distribution may be a narrower Lambertian(e.g. 60 degree FWHM), approximately Lambertian, or non-Lambertian.

In these cases, it still may be desirable to shape the incoming lightdistribution into a 2D batwing distribution, and thus it may bedesirable to optimize the design of the 2D batwing diffuser to theincoming light distribution.

Customization of the 2D batwing diffuser to achieve goals, includingspecific output distribution shapes, accommodating specific incominglight distributions, desired visual appearances, etc., can be achievedby varying many different aspects of the 2D batwing diffuser accordingto any of the embodiments described herein. Variations in geometry(including prism pitch, curvature, and geometric shape of the prismlayout), internal angle, rounding of prism peaks and valleys, surfaceroughness, etc., can be used. Prisms can be asymmetric (with agentle-sloping face on one side, and a strongly-sloped face in the otherside). The refractive index of the prisms can be varied. Higherrefractive indices may restult in wider light distribution angles andgreater degrees of nadir suppression.

Customization can include many aspects of the output light distribution,including but not limited to varying degrees of nadir suppression,different spreading angles, asymmetry, reduction of high-angleluminance, and beam bending distributions. Many of those distributionsare highly desirable to lighting designers.

In some cases, the degree of nadir suppression provided by a given 2Dbatwing diffuser may be too strong for a given incoming lightdistribution. This may be particularly true for narrower incoming lightdistributions, because nadir suppression becomes stronger as theincoming distribution becomes narrower. In addition, with some lightsources or diffuser designs, the light distribution created on thedesired flat surface may not be smooth enough.

In both of these cases it may be advantageous to add diffusion to the 2Dbatwing diffuser. If the diffusion is sufficiently strong, it willreduce the nadir suppression created by the 2D batwing diffuser, andsmooth the distribution of light projected onto a flat surface.

Adding diffusion to a 2D batwing diffuser can have the additionaldesirable effect of helping obscure light sources. This can be achievedin many ways, as illustrated in FIG. 44.

FIG. 44A shows a cross-section of a typical non-diffused embodiment forreference. The 2D batwing diffuser or light transmissive structure ofFIG. 44A includes a substrate S having first and second opposing faces40, 42 and a plurality of microprisms on the first face 40. Themicroprisms may be the microprisms in any of the embodiments describedherein such as, for example, the microprisms 12 shown in FIG. 13.

As used herein, unless the context clearly indicates otherwise, the term“2D batwing diffuser” can refer to a light transmissive structure suchas a substrate having a plurality of microprisms on a face thereof andwithout additional diffusion features, such as those diffusion featuresdescribed below in reference to FIGS. 44B-44H.

In one embodiment, depicted in FIG. 44B, diffusion is added to a 2Dbatwing diffuser according to any of the embodiments described herein bysuperimposing diffusive surface features. Many conventional surface(microstructure) diffusers include surface features such as microlensesor random roughness. Such surface features can be directly superimposedupon the surface of the prisms of the 2D batwing diffuser, and will adddiffusion to the effect of the 2D batwing diffuser.

In other embodiments, depicted in FIG. 44C, diffusion is added to a 2Dbatwing diffuser according to any of the embodiments described herein byrounding the prism tips. In related embodiments the prism tips and/orvalleys can be rounded. This rounding reduces nadir suppression andhelps obscure light sources.

In other embodiments, depicted in FIG. 44D, diffusion is added to a 2Dbatwing diffuser according to any of the embodiments described herein bycreating a conventional surface diffuser such as a microstructure orholographic diffuser on the surface of the substrate opposite the prismlayer, using techniques known in the art.

In other embodiments, depicted in FIG. 44E, diffusion is added to a 2Dbatwing diffuser according to any of the embodiments described herein byintroducing light scattering in the prism layer. This can beaccomplished for example by incorporating a scattering agent, such asminerals (e.g. TiO2 or Calcium Carbonate), microspheres or beads,particles, phase separated materials, into the liquid UV-curable polymerused to create the prism structure.

In other embodiments, depicted in FIG. 44F, diffusion is added to a 2Dbatwing diffuser according to any of the embodiments described herein byincorporating a scattering agent, such as minerals (e.g. TiO2 or CalciumCarbonate), microspheres or beads, particles, phase separated materials,into the substrate material.

In other embodiments, depicted in FIG. 44G, diffusion is added to a 2Dbatwing diffuser according to any of the embodiments described herein byconformally coating a diffusive coating onto the surface of the prisms.Diffusive coatings are known in the art, such as a mineral dispersed ina binder polymer.

In other embodiments, depicted in FIG. 44H, diffusion is added to a 2Dbatwing diffuser according to any of the embodiments described herein bycombining the transparent substrate with a diffusive layer, saiddiffusive layer comprising any conventional diffuser known in the art.

In other embodiments, not pictured, diffusion is added to a 2D batwingdiffuser according to any of the embodiments described herein by usingtwo layers separated by an air gap, said layers being a 2D batwingdiffuser and an conventional diffuser of any type. These embodimentsintroduce additional optical interfaces between air and the diffusermaterial, and thus may introduce additional reflections when used in aluminaire, reducing overall efficiency. For this reason, theseembodiments may be less preferred.

In some cases, manufacturing of the 2D batwing diffusers describedherein results in unintended variations from the desired structure. Onesuch unintended variation can be rounding of the prism peaks and valleysbeyond what is desired. For example, in the embodiment of FIG. 13, thepeaks and valleys of the prisms are substantially in the plane of thesubstrate. When these peaks and valleys are rounded by limitations ofthe manufacturing process, they present a non-negligible surface areawhich is oriented substantially parallel to the substrate. In this case,it has been experimentally observed by the applicants that thisflattening may lead to undesired ghost imaging of LED light sourcesviewed through the diffuser, and may also result in undesirableadditional light near nadir, decreasing the desired nadir suppressionprovided by the 2D batwing diffuser.

It is possible to vary the shape of the prisms to create peaks and/orvalleys that are no longer substantially parallel to the substrate toreduce these undesirable effects. This can be done for example byproviding a ramp in which the body of each prism is varied up (away fromthe underlying substrate) or down (toward the underlying substrate) asone follows the prism peak around its path. In one such embodiment, asdepicted in FIG. 45, the prisms have 60 micron pitch and followsubstantially circular paths, and are repeated in a hexagonal array tofill the surface of the diffuser. The prism internal angle is about 90degrees, and the refractive index is 1.49. The prisms are ramped up anddown at approximately 10 degree angle by an additional 20 microns inheight as depicted in the figure. When manufactured using a process thatrounds the sharp peaks and valleys and illuminated by a Lambertiansource incident up on the prism side, this 2D batwing diffuser reducesthe ghost imaging and improves the nadir suppression when compared to asimilarly designed and manufactured 2D batwing diffuser that does notinclude the ramping. In related embodiments, the variation in prism tipheight can take on forms other than a ramp, such as sinusoidal or randomvariation. Therefore, the prism height may vary along the prism path. Insome embodiments, a respective prism has a generally triangular crosssection with a pitch that varies along the prism path.

In a related embodiment, depicted in FIG. 46, the ramp angles areincreased until the shapes formed are a pyramid with substantially equalangles. It has been experimentally observed by the applicants that thisprism structure, when illuminated by a light source upon the prism side,also creates a 2D batwing light distribution, and has the additionalpotential advantage of providing a greater degree of visual hiding ofLED light sources compared a similarly designed and manufactured 2Dbatwing diffuser that does not include the pyramidal ramping.

In many cases, the exact effect of the variations in 2D batwing diffuserdesign according to any of the embodiments described herein need not bedirectly or completely understood to be optimized, because thesevariations can be readily designed using mathematical software such asMATLAB, and optimized using optical ray tracing software such asLightTools to achieve specific goals. It is possible with ray tracingsoftware to model the output of a 2D batwing diffuser according to anyof the embodiments described herein when presented with a specificincoming light distribution such as an 80 degree Lambertiandistribution. It is also possible to make a complete model of aluminaire, so as to optimize the 2D batwing diffuser design according toany of the embodiments described herein and luminaire design to achievea specific output light distribution from the luminaire.

The performance of a 2D batwing diffuser according to any of theembodiments described herein can be further varied by changing thedesign of 2D batwing diffuser across the substrate. Any of thevariations discussed above could be changed from one location toanother, or from one pattern element to another, one prism to another,to randomize the performance of the diffuser. This might be used toreduce nadir suppression in the event that it is too strong for a givenincoming light distribution, or to combine other optical functions, suchas light-source hiding, and/or visible aesthetic surface patterns.

In some embodiments, a 2D batwing diffuser according to any of theembodiments described herein includes concentric circular prismsarranged in a hexagonal repeat pattern similar to the embodiment of FIG.13. Each pattern element contains prisms of a randomly orpseudo-randomly chosen prism internal angle, ranging from 70 to 90degrees and from 80 to 100 degrees in various embodiments. The diffuserproduces a 2D batwing distribution.

Elements of Various Embodiments

Various embodiments described herein may be regarded as including thefollowing elements:

General embodiments, except for the one-big-concentric-circleembodiments:

-   -   A first textured surface    -   A second surface    -   A thickness therebetween;    -   The textured surface comprising    -   A microprism array, the microprism array comprising a plurality        of microprisms with substantially more than one prism        orientation angle,

The microprism array being conceptually divisible into at least 10sub-areas for which each sub-area contains prismatic microstructureswith a substantially the same distribution prism orientation angles asthe other sub-areas.

Embodiment 1 focuses on the concentrics:

1. A two-dimensional batwing diffuser comprising

-   -   A first textured surface    -   A second surface    -   A thickness therebetween;    -   The textured surface comprising    -   A microprism array, the microprism array comprising a plurality        of elements, each element comprising prismatic microstructures        arranged in a concentric geometric shape;    -   The prismatic microstructures having substantially more than one        prism orientation angle.

Embodiment 2 focuses on the “parallel” aspect, that even in concentriccircles, they're essentially parallel prisms.

2. A two-dimensional batwing diffuser comprising

-   -   A first textured surface    -   A second surface    -   A thickness therebetween;    -   The textured surface comprising    -   A microprism array, the microprism array comprising a plurality        of elements, each element comprising prismatic microstructures        arranged substantially parallel to one another;    -   The prismatic microstructures having substantially more than one        prism orientation angle.

Additional embodiments:

3. A two-dimensional batwing diffuser comprising

-   -   A first textured surface    -   A second surface    -   A thickness therebetween;    -   The textured surface comprising    -   A microprism array, the microprism array comprising a plurality        of small areas on the substrate, each area on the substrate        comprising prismatic microstructures with more than one prism        orientation angle, in which at least some portion of the        prismatic microstructures have a prism orientation angle that is        at an angle of at least 45 degrees from the prism orientation        angle of prismatic microstructures in another portion of the        area.        4. Embodiment (3) Where the angle difference is at least 60        degrees        5. Embodiment (3) Where the angle difference is 90 degrees        6. Embodiments (3, 4, or 5) where “small” areas are less than        1-4 square centimeters in 2D projected surface area.        7. Embodiments (1 through 5) where the prism internal angle        between 70 and 110 degrees or between 60 and 100 degrees, prism        pitch between 10 microns and 3 millimeters.        8. Embodiments (1 through 5) where the Prism internal angle is        between 70 and 90 degrees or between 80 and 100 degrees, prism        pitch between 10 microns and 1 millimeter.        9. Embodiments (1 through 5) where the second surface is smooth        10. Embodiments (1 through 5) second surface is diffusive with        diffusion angle less than about 60 degrees FWHM        11. Embodiments (1 through 5) where the more than one prism        orientation angles includes at least 0, 45, 90, and 135 degrees        12. Embodiments (1 through 5) where the more than one prism        orientation angles encompasses substantially all angles in the        plane of the first textured surface        13. Embodiment 12, where the plurality of prismatic        microstructures has a distribution of prism orientation angles        that is substantially uniform over all angles in the plane        (creates a circularly symmetric distribution)        14. Embodiment 12, where the plurality of prismatic        microstructures has a distribution of prism orientation angles        with a substantial portion near a first angle, and another        substantial portion of the prism orientation angles near a        second angle that differs by at least 45 degrees from the first        angle (this creates a somewhat rectangular distribution)        15. Embodiment 14, where the prism internal angle is varied as a        function of prism orientation angle (this makes the rectangular        distribution more rectangular) (FIG. 18—better        rectangular/square distribution)        16. Embodiment 14, above where the second angle differs by 90        degrees from the first angle (this creates a square        distribution)        17. Embodiments comprising collections of linear prisms (such as        FIGS. 29,30)        a. Deterministic or random        18. A two-dimensional batwing diffuser comprising    -   A first textured surface    -   A second surface    -   A thickness therebetween;    -   The textured surface comprising    -   A microprism array, the microprism array comprising a plurality        of elements with area on the substrate of less than 1 square        inch, each element on the substrate comprising prismatic        microstructures arranged in a concentric geometric shape.        19. Embodiment 18, in which the concentric geometric shape is        substantially an ellipse.        20. Embodiment 19, in which the elliptical concentric geometric        shape is substantially a circle.        21. Embodiment 18, in which the concentric geometric shape is        substantially a rhombus.        22. Embodiment 21, in which the concentric geometric shape is        substantially a square.        23. Embodiment 18, in which the concentric geometric shape is        substantially a shape that fits between a rectangle and its        inscribed ellipse.        24. Embodiment 18, in which the concentric geometric shape is a        shape that fits between a square and its inscribed circle.        25. Embodiment 18, in which the concentric geometric shape is a        shape that fits between a rhombus and its inscribed ellipse.        26. Embodiments 18 through 25, in which the prism internal angle        is varied as a function of the prism orientation angle.        27. Embodiment 22, in which the prism internal angle is varied        as a function of the prism orientation angle.        28. Embodiment 27, in which the prism internal angle for a prism        of a given orientation angle is smaller in inverse proportion to        the prevalence of the given orientation angle in terms of        substrate surface area.        29. An embodiment related to random continuous orientations of        prisms (FIGS. 21,22)        30. An embodiment related to first surface prisms having        additional roughness (to create diffusion)        31. An embodiment related to first surface deviates from a prism        shape (curved sides, or rounded peaks or valleys) to create        diffusion        32. A luminaire with two-dimensional batwing light distribution        employing the two-dimensional batwing diffuser of any of the        embodiments.        33. A luminaire with two-dimensional one-sided batwing light        distribution employing the two-dimensional batwing diffuser of        any of the embodiments.        34. A method of forming a two-dimensional batwing light        distribution by passing light through the two-dimensional        diffuser of any of the embodiments.        35. Embodiments where either side of the material is further        embedded in another material.

Various embodiments have been described above with reference to theaccompanying drawings. Other embodiments may take many different formsand should not be construed as limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art.

When an element is referred to as being on, coupled or connected to/withanother element, it can be directly on, coupled or connected to/with theother element or intervening elements may also be present. In contrast,if an element is referred to as being directly on, coupled or connectedto/with another element, then no other intervening elements are present.As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. The symbol “/” is also usedas a shorthand notation for “and/or”.

It will be understood that although the terms first and second are usedherein to describe various regions, layers and/or sections, theseregions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one region, layer or sectionfrom another region, layer or section. Thus, a first region, layer orsection discussed above could be termed a second region, layer orsection, and similarly, a second region, layer or section could betermed a first region, layer or section without departing from theteachings of the present invention. Like numbers refer to like elementsthroughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” “includes” and/or “including”, “have” and/or“having” (and variants thereof) when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

What is claimed is:
 1. A light transmissive structure comprising: alight transmissive substrate having first and second opposing faces; andan array of microprism elements on the first face, a respectivemicroprism element comprising a plurality of concentric microprisms;wherein the light transmissive structure is configured to receive lightfroth a light source facing the first face and distribute the lightemerging from the second face in a 2D batwing distribution.
 2. The lighttransmissive structure of claim 1 wherein the array of microprismelements extends over substantially the entire first face of thesubstrate.
 3. The light transmissive structure of claim 1 wherein arespective microprism element comprises a plurality of concentriccircular microprisms.
 4. The light transmissive structure of claim 3wherein a respective microprism element is generally hexagonal.
 5. Thelight transmissive structure of claim 3 wherein a respective microprismelement is generally square.
 6. The light transmissive structure ofclaim 3 wherein at least some of the microprisms have a generallytriangular cross section with a peak, the cross section taken in a planeperpendicular to the first face of the substrate, and have a prisminternal angle defined by the peak that varies as a function of a prismorientation angle that is measured relative to an edge of the substrate.7. The light transmissive structure of claim 6 wherein portions of themicroprisms having prism orientation angles of about 45 degrees and 135degrees have a prism internal angle that is less than a prism internalangle of portions of the microprisms having prism orientation angles ofabout 0 degrees and 90 degrees.
 8. The light transmissive structure ofclaim 1 wherein a respective microprism element comprises a plurality ofconcentric elliptical microprisms.
 9. The light transmissive structureof claim 1 wherein a respective microprism element comprises a pluralityof concentric rounded square microprisms.
 10. The light transmissivestructure of claim 9 wherein a respective microprism element isgenerally square.
 11. The light transmissive structure of claim 9wherein a respective rounded square microprism has a shape that fitsbetween a square and its inscribed circle.
 12. The light transmissivestructure of claim 9 wherein at least some of the microprisms have agenerally triangular cross section with a peak, the cross section takenin a plane perpendicular to the first face of the substrate, and have aprism internal angle defined by the peak that varies as a function of aprism orientation angle that is measured relative to an edge of thesubstrate.
 13. The light transmissive structure of claim 12 whereinportions of the microprisms having prism orientation angles of about 45degrees and 135 degrees have a prism internal angle that is less than aprism internal angle of portions of the microprisms having prismorientation angles of about 0 degrees and 90 degrees.
 14. The lighttransmissive structure of claim 1 wherein a respective microprismelement comprises a plurality of concentric rounded rhombus microprisms.15. The light transmissive structure of claim 14 wherein a respectiverounded rhombus microprism has a shape that fits between a rhombus andits inscribed ellipse.
 16. The light transmissive structure of claim 14wherein at least some of the microprisms have a generally triangularcross section with a peak, the cross section taken in a planeperpendicular to the first face of the substrate, and have a prisminternal angle defined by the peak that varies as a function of a prismorientation angle that is measured relative to an edge of the substrate.17. The light transmissive structure of claim 1 wherein a respectivemicroprism element comprises concentric microprisms of random orpseudorandom size and/or shape.
 18. The light transmissive structure ofclaim 1 wherein a respective microprism element is longer in a firstdirection along the substrate than in a second, orthogonal directionalong the substrate.
 19. The light transmissive structure of claim 1wherein a respective microprism element has an area of less than about 1square centimeter on the second face of the substrate.
 20. The lighttransmissive structure of claim 1 wherein a respective microprismelement has an area of about 0.1 square centimeters or less on thesecond face of the substrate.
 21. The light transmissive structure ofclaim 1 wherein a respective microprism is undetectable by the nakedeye.
 22. The light transmissive structure of claim 1 wherein at leastsome of the microprisms have a generally triangular cross section with apeak, the cross section taken in a plane perpendicular to the first faceof the substrate.
 23. The light transmissive structure of claim 22wherein the peak is generally parallel to the first face of thesubstrate.
 24. The light transmissive structure of claim 22 wherein thepeak is a sharp peak.
 25. The light transmissive structure of claim 22wherein the peak is a rounded peak.
 26. The light transmissive structureof claim 22 wherein: a respective microprism has an internal angledefined by the peak of between about 60 and 100 degrees; and arespective microprism has a pitch of between about 10 microns and 3 mm.27. The light transmissive structure of claim 22 wherein: a respectivemicroprism has an internal angle of between about 70 and 90 degrees; anda respective microprism has a pitch of between about 10 microns and 1mm.
 28. The light transmissive structure of claim 1 whereinsubstantially all of the microprism elements comprise a plurality ofconcentric microprisms.
 29. The light transmissive structure of claim 1wherein adjacent microprism elements are in contact with one another.30. The light transmissive structure of claim 1 wherein the array ofmicroprism elements comprises gaps between at least some of themicroprism elements, the light transmissive structure further comprisinggap-filling microstructures in at least some of the gaps.
 31. The lighttransmissive structure of claim 1 wherein at least some of themicroprisms have a generally triangular cross section with a peak, thecross section taken in a plane perpendicular to the first face of thesubstrate, the peak having a height relative to the first face of thesubstrate that varies as a function of a prism orientation angle that ismeasured relative to an edge of the substrate.
 32. The lighttransmissive structure of claim 1 wherein the light transmissivestructure is configured to receive light having a Lambertiandistribution from a light source facing the first face and distributethe light emerging from the second face in a 2D batwing distribution.33. The light transmissive structure of claim 1 wherein the lighttransmissive structure is configured to receive light having a lightdistribution having a Full Width at Half Maximum (FWHM) of at leastabout 30 degrees from a light source facing the first face anddistribute the light emerging from the second face in a 2D batwingdistribution.
 34. The light transmissive structure of claim 1 whereinthe light transmissive structure is configured to receive light having alight distribution having a Full Width at Half Maximum (FWHM) of atleast about 40 degrees from a light source facing the first face anddistribute the light emerging from the second face in a 2D batwingdistribution.
 35. The light transmissive structure of claim 1 whereinthe light transmissive structure is configured to receive light having alight distribution having a Full Width at Half Maximum (FWHM) of atleast about 60 degrees from a light source facing the first face anddistribute the light emerging from the second face in a 2D batwingdistribution.
 36. The light transmissive structure of claim 1 whereinthe light transmissive structure is configured to receive light having alight distribution having a Full Width at Half Maximum (FWHM) of atleast about 80 degrees from a light source facing the first face anddistribute the light emerging from the second face in a 2D batwingdistribution.
 37. The light transmissive structure of claim 1 furthercomprising at least one diffusion feature, wherein the lighttransmissive structure is configured to receive collimated and/ornear-collimated light from a light source facing the first face anddistribute the light emerging from the second face in a 2D batwingdistribution.
 38. The light transmissive structure of claim 37 whereinthe diffusion feature comprises surface roughness on at least some ofthe microprisms.
 39. The light transmissive structure of claim 37wherein the diffusion feature comprises a diffuser on the second face ofthe substrate.
 40. The light transmissive structure of claim 37 whereinthe diffusion feature comprises a light scattering agent in at leastsome of the microprisms and/or in the substrate.
 41. The lighttransmissive structure of claim 37 wherein the diffusion featurecomprises a diffusive coating on at least some of the microprisms. 42.The light transmissive structure of claim 1, wherein a respectivemicroprism follows a prism path along the first face of the substrate,wherein the microprism has a generally triangular cross section with apeak and a pitch, the cross section taken in a plane perpendicular tothe first face of the substrate, and wherein: (i) the peak has a heightrelative to the first face of the substrate that varies along the prismpath; and/or (ii) the pitch varies along the prism path.
 43. The lighttransmissive structure of claim 1 in combination with at least one lightsource and a housing that is configured to hold the at least one lightsource and the light transmissive substrate so that light from the lightsource impinges on the first face of the substrate and emerges from thesecond face of the substrate in a 2D batwing distribution.
 44. Thecombination of claim 43 wherein the housing defines a light exit surfacearea where the substrate is held, and wherein a respective microprismelement has an area on the first face of the substrate that is at leastone order of magnitude smaller than the light exit surface area.
 45. Thecombination of claim 44 wherein a respective microprism element has anarea on the first face of the substrate that is at least two orders ofmagnitude smaller than the light exit surface area.
 46. The combinationof claim 44 wherein a respective microprism element has an area on thefirst face of the substrate that is at least four orders of magnitudesmaller than the light exit surface area.
 47. The combination of claim43 wherein the housing defines a light exit surface area where thesubstrate is held, and wherein the array of microprism elements on thefirst face of the substrate extends over substantially the entire lightexit surface area.
 48. The combination of claim 43 wherein the lightsource is an array of LEDs with a spacing between adjacent LEDs, andwherein a respective microprism element has a size that generallycorresponds to the spacing between adjacent LEDs.
 49. The lighttransmissive structure of claim 1 in combination with at least one lightsource wherein the light transmissive substrate is suspended under thelight source so that light from the light source impinges on the firstface of the substrate and emerges from the second face of the substratein a 2D batwing distribution.
 50. A method of fabricating a lighttransmissive structure, the method comprising: imaging onto aphotoimageable material an image of a plurality of microprisms having ageometric feature that is configured to distribute light transmittedthrough the microprisms in a 2D batwing distribution; and using thephotoimageable material that was imaged to replicate an image of aplurality of microprisms in and/or on a substrate, the plurality ofmicroprisms also having a geometric feature that is configured todistribute light transmitted through the microprisms in a 2D batwingdistribution.
 51. The method of claim 50 wherein the imaging comprisesscanning a laser across the photoimageable material, the laser definingthe image of a plurality of microprisms having the geometric featurethat is configured to distribute light transmitted through themicroprisms in a 2D batwing distribution.
 52. A light transmissivestructure comprising: a light transmissive substrate having first andsecond opposing faces; and a plurality of microprisms on the first face,the microprisms having a generally triangular cross section in a planethat is perpendicular to the first face, wherein the microprisms aredistributed on the first face of the substrate in a plurality ofdifferent prism orientation angles measured from an edge of thesubstrate; wherein the light transmissive structure is configured toreceive light having a Full Width at Half Maximum (FWHM) of at leastabout 30 degrees and/or Lambertian light at the first face anddistribute the light emerging from the second face in a 2D batwingdistribution.
 53. The light transmissive structure of claim 52 whereinthe microprisms are distributed on the first face of the substrategenerally equally in each of the plurality prism orientation angles. 54.The light transmissive structure of claim 52 wherein microprisms havinga prism orientation angle of about 45 and 135 degrees are distributed ona greater area of the first face of the substrate than microprismshaving a prism orientation angle of about 0 and 90 degrees.
 55. Thelight transmissive structure of claim 52 wherein the microprisms have aninternal angle that varies as a function of prism orientation angle. 56.The light transmissive structure of claim 52 wherein the plurality ofmicroprisms and/or interspersed microstructures substantially cover thefirst face of the substrate.
 57. A light transmissive structurecomprising: a light transmissive substrate having first and secondopposing faces; and an array of microprism elements on the first face, arespective microprism element comprising a plurality of concentricmicroprism patterns, a respective microprism pattern comprising aplurality of pyramids arranged in a generally elliptical configuration;wherein the light transmissive structure is configured to receive lightfrom a light source facing the first face and distribute the lightemerging from the second face in a 2D batwing distribution.